Patent Description:
Electromechanical driving elements have in prior art been used for many types of miniature motor applications. A large portion of these motors is based on ultrasonic operation of the electromechanical driving elements. Typical examples of electromechanical materials are piezoelectric, electrostrictive, and antiferroelectric materials and these materials could be single crystalline as well as polycrystalline or amorphous.

Piezoelectric materials are popular to use due to the relative simplicity in activation of the piezoelectric effect. Many different designs are available. In the PiezoWave® motor, a piezoelectric bar is put into resonance. A drive pad on the bar is in contact with a body to be moved, and the motion of the drive pad is transferred into a moving action relative the body to be moved. This is a compact solution that has been advantageously used in many types of applications.

In the published international patent applications <CIT> and <CIT>, motors that comprise piezo elements that create vibration of a sheet metal through a less rigid portion are disclosed. This connecting portion thus works as a link between the resonators and may by proper designs withstand high preloads without involving the piezo elements.

Common for many of these types of motors is that a contact point of a stator is moved repeatedly in a closed loop. Typically, the loop corresponds to a path close to an elliptical path if the contact point is allowed to move without external interactions. However, the interaction between the moving contact point and the body to be moved creates the total motion. During one part of the loop, the contact point is in mechanical contact with the body to be moved and interacts with the body to achieve the requested motion thereof. During another part of the loop, the contact point is instead free from mechanical contact and may thereby be "reset" to prepare for a new driving contact. In order for such a driving scheme to be operable, a normal force has to be provided between the stator and the body to be moved. This normal force presses the stator against the body to be moved. The motion of the contact point is typically very fast and the inertia of the stator enables the contact point to be temporarily removed completely from the surface of the body to be moved, if an appropriate normal force is applied. Too high or too low applied normal forces typically give a non-optimum operation. It is therefore a request to select a proper, well-defined, normal force in order to achieve an efficient motion.

Piezoelectric motors are often used in miniaturized systems, which puts further restrictions to the arrangements providing the normal forces.

In the published patent application <CIT>, an oscillation wave driver comprises a piezoelectric oscillator where a piezoelectric body is fixed to a resilient body, and a member coming into pressure contact with the piezoelectric oscillator. The resilient body is provided integrally with parts for imparting a pressing force to the piezoelectric oscillator and resilient body. The resilient body itself is provided with a part for generating the pressing force and integrated with the parts for imparting the pressing force.

In the published patent application <CIT>, an ultrasonic motor is disclosed, constituted of a base section composed of a bar-like elastic body, a beam section composed of an elastic body integrally formed with the base section so that the elastic body can be perpendicularly protruded from the nearly central part of the base section, and at least two electromechanical energy converting elements which are provided in the base section on both sides of the section. These electromechanical energy converting elements cause the base section to generate flexural vibrations. The motor is also provided with an ultrasonic vibrator which causes flexural vibrations on both sides of the beam section by respectively applying alternating voltages having a fixed phase difference between them across the elements, supporting sections which are extended from points near the nodes of vibrations at both ends of the vibrator, and a traveling body which is press-contacted with the front end of the beam section and pressed by the elastic deformation of the bottom section which is part of the supporting section. The resonance frequency of the vibrator is made different from that of the supporting section.

A general object is to provide electromechanical motors which enables use of well-defined normal forces within a limited space.

The above object is achieved by devices according to independent claim Preferred embodiments are defined in the dependent claims.

In general words, in a first aspect, an electromechanical stator comprises an actuator section, a support section, and a spring section. A continuous sheet of elastic material constitutes at least a part of the actuator section, at least a part of the support section, and at least a part of the spring section. The actuator section comprises a vibration assembly comprising at least one vibration body and a moved-body interaction portion. The vibration body comprises an electromechanical volume attached to a part of the continuous sheet of elastic material, wherein the vibration body is adapted to cause bending vibrations, in a vibration direction transverse to the plane of the continuous sheet of elastic material, when alternating voltages are applied to the electromechanical volume. The support section is attached between the actuator section and the spring section. The support section is connected with at least one fixation point via the spring section. The spring section is elastic, with a spring constant, regarding displacements, in the vibration direction, of the fixation point relative to a connection point between the spring section and the support section, thereby enabling provision of a normal force in the vibration direction on the moved-body interaction portion upon displacement of the fixation point in the vibration direction. The continuous sheet of elastic material of the spring section has a pattern of cuts, providing at least one limited path between connection points to the support section and the at least one fixation point.

In a second aspect, an electromechanical motor comprises an electromechanical stator according to the first aspect, a body to be moved, and a voltage supply adapted to supply alternating voltages to the electromechanical volume of said vibration body.

One advantage with the proposed technology is that well-defined normal forces and other operational conditions are provided by arrangements that are limited in space. Other advantages will be appreciated when reading the detailed description.

The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:.

Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

For a better understanding of the proposed technology, it may be useful to begin with a brief overview of some basic considerations concerning operation of ultrasonic electromechanical motors.

<FIG> illustrates schematically an actuator section <NUM> of an electromechanical motor, having a vibration assembly <NUM>. The vibration assembly <NUM> comprises a vibration body <NUM>, in turn comprising an electromechanical volume <NUM> of electromechanically active material, which vibration body <NUM> causes vibrations when alternating voltages are applied to the electromechanical volume <NUM>. The vibration assembly <NUM> further comprises a moved-body interaction portion <NUM>, which is intended to be the part of the electromechanical stator interacting with the body to be moved. The total resilience <NUM> of the vibration assembly is indicated by a spring-like part in the figure.

If proper alternating voltages are provided to the electromechanical volume <NUM>, the vibration body <NUM> can be caused to start to vibrate and the moved-body interaction portion <NUM> can typically be caused to move along a closed loop path <NUM>, as schematically illustrated in <FIG>. This motion is then used in the electromechanical motor for achieving the displacement of the body to be moved. The actual details of how to achieve the closed loop path depends on the actual design of the vibration assembly <NUM> and is, as such, well known in prior art. The motion component in the X-direction close to the top of the closed loop path <NUM> can be used in mechanical interaction with the body to be moved to transfer a displacement force in the X direction. At the contrary, when the motion component in the negative X-direction close to the bottom of the closed loop path <NUM> is present, any mechanical interaction with the body to be moved should be avoided. The necessary function of providing and removing the mechanical contact with the body to be moved is performed by the motion component in the Z direction. This Z-direction movement will be the main subject of the present disclosure.

In <FIG>, a diagram illustrating an embodiment periodic behaviour of the Z-direction component <NUM> along the closed loop path is illustrated, when the vibration body <NUM> is operating without any normal force, i.e. without any contacts with any body to be moved. The top parts of the curve corresponds to phases where there is a positive X motion component and the bottom parts of the curve corresponds to phases where there is a negative X motion component. It is therefore requested to use the Z-direction motion to contact and remove the contact, respectively, to the body to be moved.

Typically, the applied voltages can also be provided to give a closed loop path in the opposite direction.

As mentioned above, in order to transform the motion of the moved-body interaction portion <NUM> into a displacement of the body to be moved, the moved-body interaction portion <NUM> has to mechanically interact with the body to be moved. <FIG> illustrates schematically an electromechanical stator <NUM> of an electromechanical motor <NUM>. The actuator section <NUM> is pressed against the body <NUM> to be moved with a normal force F, applied by a spring section <NUM>. The force F is applied essentially perpendicular to the motion direction, which is the explanation of the name. A support section <NUM> may be present as a bridge between the actuator section <NUM> and the spring section <NUM>. The total resilience <NUM> of the spring section <NUM>, and optionally also the support section <NUM>, is indicated by a spring-like part in the figure.

If a low-frequency alternating voltage is applied to the vibration body <NUM>, the spring section <NUM> will compensate for the achieved vibrations. The moved-body interaction portion <NUM> will be in constant mechanical contact with the body <NUM> to be moved. This results in that the entire electromechanical stator <NUM> will just slowly vibrate without causing any movements at all. However, if the frequency of the provided alternating voltage is increased, the inertia of the system will start to play an important role. When the vibration of the vibration body <NUM> causes the moved-body interaction portion <NUM> to move in the negative Z-direction, i.e. away from the body <NUM> to be moved, the inertia of the electromechanical stator <NUM> will prevent the spring section <NUM> to compensate the motion immediately. The result is that the moved-body interaction portion <NUM> leaves the mechanical contact with the body <NUM> to be moved for a short period of time. During this time, the moved-body interaction portion <NUM> can freely move e.g. in the negative X direction without interfering with the body <NUM> to be moved. In other words, the moved-body interaction portion <NUM> can be reset and prepare for a new contact with the body <NUM> to be moved without having any mechanical contact with the body to be moved.

<FIG> is a schematic diagram illustrating a movement <NUM> of a Z direction position zem of a connection point between the spring section <NUM> (or support section <NUM>) and the actuator section <NUM>. This connection point is in the following referred to as the frame support point. When the contact between the moved-body interaction portion <NUM> and the body <NUM> to be moved is removed, the normal force provided by the spring section <NUM> will start to move the actuator section <NUM> towards the body <NUM> to be moved. The inertia of the system will give this motion a much longer time constant than the vibrations of the actuator section <NUM>. The motion of the above mentioned connection point will continue until the moved-body interaction portion <NUM> again meets the body <NUM> to be moved, which typically occurs when the vibration of the actuator section <NUM> moves the moved-body interaction portion <NUM> towards the body <NUM> to be moved again. The frame support point will then be pushed back again, typically to the original position. The stroke of this movement depends on the size of the normal force, the mass of the moving parts and the frequency of the actuator section <NUM> vibrations.

<FIG> is a schematic diagram illustrating the position <NUM> in Z direction of the tip of the moved-body interaction portion <NUM> during operation. The diagram starts at the time when the actuator section <NUM> pulls the moved-body interaction portion <NUM> away from the body <NUM> to be moved. The moved-body interaction portion <NUM> performs the bottom part of the closed loop, c. <FIG>, however corrected by the movement of the frame support point. In the meantime, the frame support point is slowly moved in the positive Z direction, as indicated by the dotted line <NUM>. Since such a movement results in bringing the moved-body interaction portion <NUM> and frame support points closer, the dotted line <NUM> corresponds to the negative frame support point movement. These motions continues until the moved-body interaction portion <NUM> again reaches the body <NUM> to be moved at the point <NUM>, which corresponds to the point where the curve <NUM> and the negative correspondence of curve <NUM>, i.e. curve <NUM>, meet. In other words, zip equals the position zb of the surface of the body <NUM> to be moved. The contact with the body <NUM> to be moved prohibits any further motion in the Z direction of the moved-body interaction portion <NUM> and during the remaining part of the period, only the frame support point slowly returns to the original position again, by action of the force applied in the Z direction by the actuator section <NUM>, which is illustrated by the curve section <NUM>. The process then starts all over again.

It can now be understood that the relation between the time constants of the two motions, i.e. the actuator section <NUM> vibration as illustrated by the curve <NUM> and the movement <NUM> of the frame support point, plays an important role for the operation of the motor. If the time constant of the frame support point movement <NUM> decreases relative to the time constant of the actuator section <NUM> vibration, i.e. the motion of the frame support point is relatively faster, the time period during which the moved-body interaction portion <NUM> is free from contact with the body <NUM> to be moved is reduced. This is schematically illustrated by the dotted curve <NUM>. This means that the moved-body interaction portion <NUM> may be in contact with the body <NUM> to be moved also during phases of the vibration when there is a non-negligible motion component in the negative X direction. This in turn reduces the speed and increases the wear.

Likewise, if the time constant of the frame support point movement <NUM> increases relative to the time constant of the actuator section <NUM> vibration, i.e. the motion of the frame support point is relatively slower, the time period during which the moved-body interaction portion <NUM> is in contact with the body <NUM> to be moved is reduced. This is schematically illustrated by the dotted curve <NUM>. This means that the moved-body interaction portion <NUM> may influence the body <NUM> to be moved during a shorter period of time, which in turn reduces the available speed. Furthermore, also the available force in the X direction movement is reduced.

In order to optimize the operation of the motor, the applied normal force is preferably adapted to fit properly to the operation frequency and to the different masses of the different parts of the motor. There is thus requested that the spring section has well-defined and easy controllable elasticity properties. At the same time, since the typical ultrasonic electromechanical motors are applied in miniature applications, such spring sections have to be provided within a limited space and preferably requesting as few mounting steps as possible.

According to the technology presented in the present disclosure, a continuous sheet of elastic material can be used as a basic part for an actuator section, a support section as well as for a spring section. This minimizes required mounting efforts and increases a mounting accuracy. At the same time, just by appropriate designing the shape of the continuous sheet of elastic material, appropriate properties of the different sections can be achieved. A well controllable normal force can easily be achieved in a direction transverse to the main plane of the continuous sheet of elastic material.

In one embodiment, an electromechanical stator comprises an actuator section, a support section and a spring section. A continuous sheet of elastic material constitutes at least a part of the actuator section, at least a part of the support section and at least a part of the spring section. The actuator section comprises a vibration assembly in turn comprising at least one vibration body and a moved-body interaction portion. The vibration body comprises an electromechanical volume attached to a part of the continuous sheet of elastic material. The vibration body is arranged for causing bending vibrations, in a vibration direction transverse to the plane of the continuous sheet of elastic material, when alternating voltages are applied to the electromechanical volume. The support section is attached between the actuator section and the spring section. The support section is connected with at least one fixation point via the spring section. The spring section is elastic, with a spring constant, regarding displacements, in the vibration direction, of the fixation point relative to a connection point between the spring section and the support section, thereby enabling provision of a normal force in the vibration direction on the moved-body interaction portion upon displacement of the fixation point in the vibration direction.

<FIG> illustrates one embodiment of an electromechanical stator <NUM>. The electromechanical stator <NUM> comprises an actuator section <NUM>, at least one support section <NUM> and at least one spring section <NUM>. In this embodiment, the electromechanical stator <NUM> comprises two support sections <NUM> and two spring sections <NUM>, provided on opposite sides of the actuator section <NUM>. A continuous sheet of elastic material <NUM> constitutes at least a part of the actuator section <NUM>, at least a part of the support sections <NUM> and at least a part of the spring sections <NUM>.

The actuator section <NUM> comprises a vibration assembly <NUM> in turn comprising at least one vibration body <NUM> and a moved-body interaction portion <NUM>. In this embodiment, the vibration assembly <NUM> comprises two vibration bodies <NUM>, interconnected by the moved-body interaction portion <NUM>. The vibration bodies <NUM> each comprises an electromechanical volume <NUM> attached to a part of the continuous sheet of elastic material <NUM>. The vibration bodies <NUM> are arranged for causing bending vibrations, in a vibration direction Z transverse to the plane of the continuous sheet of elastic material <NUM>, when alternating voltages are applied to the respective electromechanical volumes <NUM>. The actuator section <NUM> is connected to the support sections <NUM> on its sides by attachment members <NUM>.

The part of the continuous sheet of elastic material <NUM> that constitutes the spring section <NUM> is elastic concerning movements in the Z direction. In a state free from elastic deformation, i.e. where the continuous sheet of elastic material <NUM> of the spring section <NUM> is not exposed for any elastic displacements in the Z direction, the continuous sheet of elastic material <NUM> of the spring section <NUM> is flat. Such a situation is illustrated in <FIG>.

Each support section <NUM> is attached between the actuator section <NUM> and a respective spring section <NUM>. The aim of the support section <NUM> is to decouple any motions, in particular rotational motions, induced by the actuator section <NUM>, from being transferred into the spring section <NUM>. The actuator section <NUM> performs bending vibrations, which typically cause the attachment members <NUM> to twist or rotate. However, since the twisting properties of the main support section <NUM> is far less admitting, any rotation motions, mainly around an axis within the continuous sheet of elastic material <NUM>, of the attachment members <NUM> will not be transferred over to the spring section <NUM>. Therefore, the support section <NUM> is preferably adapted for at least partially prohibiting rotational movements of the actuator section <NUM> to propagate to the spring section <NUM>.

The spring sections <NUM> connect a respective support section <NUM> with at least one fixation point <NUM>. Each spring section <NUM> is elastic, with a spring constant, regarding displacements of the fixation point <NUM> in the vibration direction Z relative to a connection point between the spring section <NUM> and the support section <NUM>. This elasticity thereby enabling provision of a normal force in the vibration direction Z on the moved-body interaction portion <NUM> upon displacement of the fixation point <NUM> in the vibration direction Z. <FIG> illustrates such a situation, when the fixation point <NUM> has been displaced a distance D causing an elastic deformation of the continuous sheet of elastic material <NUM> of the spring section <NUM> resulting in that the actuator section <NUM> and in particular the moved-body interaction portion <NUM> is pushed upwards in the figure with a force that will be used as the normal force when mounted in a motor. <FIG> thus illustrates the embodiment of an electromechanical stator in a state before mounting it in an electromechanical motor, while <FIG> illustrates the same embodiment in a condition similar to what it looks like when it is mounted in an electromechanical motor.

The actuator section <NUM> will typically expose the attachment members <NUM> for different kinds of vibrations. It is preferred if at least the high-frequency parts of these vibrations are not propagating the whole way to the fixation points <NUM>. Due to the fundamentally differing geometrical dimensions of the supporting section <NUM> compared to the attachment members <NUM>, a large portion of the vibration energy provided to the attachment members <NUM> will be reflected back to the actuator section <NUM>. Furthermore, due to the fact that the spring section <NUM> and the support section <NUM> together has a relatively high inertia, the elastic behaviour of the spring section <NUM> will also give rise to a low-pass filter action. In other words, the support section <NUM> and the spring section <NUM> together constitutes a low-pass filter of vibrations between the actuator section <NUM> and said fixation point <NUM>.

In this particular embodiment, the continuous sheet of elastic material <NUM> of the spring section <NUM> has a pattern of cuts <NUM>. These cuts <NUM> remove the direct paths through the continuous sheet of elastic material <NUM> from the support section <NUM> to the fixation point <NUM>, which means that the efficient length of a path <NUM> from the support section <NUM> to the fixation point <NUM> becomes much longer. Since the elastic properties of the spring section <NUM> is dependent, among other parameters, on such a length, the spring constant of the spring section <NUM> can be reduced without extending the spring section <NUM> laterally, cf. <FIG> further below. In other words, the cuts <NUM> provide at least one limited path <NUM> between connection points <NUM> to the support section <NUM> and the fixation point <NUM>. In the present embodiment, this at least one limited path <NUM> is curved.

Furthermore, the limited path <NUM> created by the cuts <NUM> has also typically a smaller width, at least in comparison with paths through the supporting section <NUM>. In other words, at least one limited path <NUM> has a smaller average cross-section area than an average cross-section along a closest path between the connection points <NUM> between the spring section <NUM> and the support section <NUM> and the attachment members <NUM> between the actuator section <NUM> and the support section <NUM>. A smaller width, or rather a smaller cross-section is typically associated with a lower spring constant. This results in that the spring section <NUM> becomes the dominating part in determining the overall spring properties of the electromechanical stator <NUM>.

The continuous sheet of elastic material is in a typical embodiment a flat metal sheet. However, there are also other possible designs and/or compositions of the continuous sheet of elastic material.

In one embodiment, the continuous sheet of elastic material has an essentially homogeneous composition throughout the sheet. In other words, one and the same material forms the entire sheet.

In another embodiment, the continuous sheet of elastic material changes its composition over the sheet area. This may be provided e.g. by using materials having a chemical gradient over the sheet area, or by applying different treatments, e.g. hardening or coatings, on different parts of the sheet. In such a way, the material properties may be somewhat adapted for the different sections. A more rigid material may e.g. be useful in the support section in certain applications. A softer material may instead be beneficial in the spring section, depending on the technical fields of application.

However, in order to achieve some of the benefits of the continuous sheet of elastic material, the continuous sheet of elastic material should be provided in one permanently joined piece. Gradients or other changed properties may in certain embodiments be provided by starting out from separate pieces that then are unified into one piece by an irreversible joint. In other embodiments, gradients or changed properties may be achieved in an initially homogeneous material. In further embodiments, gradients or changed properties in the continuous sheet of elastic material may be provided in connection with the manufacturing of the material itself.

The electromechanical stator <NUM> is intended to be incorporated in an electromechanical motor. <FIG> illustrates an embodiment of an electromechanical motor <NUM> having an electromechanical stator according to the embodiment of <FIG>. The electromechanical motor <NUM> further comprises a body <NUM> to be moved and a voltage supply <NUM> arranged to supply alternating voltages to the electromechanical volume <NUM> of the vibration bodies <NUM>. This particular embodiment also comprises a bearing arrangement <NUM>, which defines the position of the fixation point <NUM> relative to the body <NUM> to be moved. Note that the drawings typically are enlarged compared to the actual size. A typical size of an electromechanical motor of this kind is a few millimetres.

<FIG> illustrates another embodiment of an electromechanical motor <NUM>, where two electromechanical stators <NUM> according to the <FIG> are mounted in a twin design on opposite sides of the body <NUM> to be moved. By attaching the fixation points <NUM> of the two electromechanical stators <NUM> to each other by fixation means <NUM>, possibly via a distance element, the need for any bearing arrangement vanishes. Instead, the two electromechanical stators <NUM> can be operated synchronized with each other. The fixation means <NUM> can be of any kind providing a temporary or permanent mechanical connection. Typical examples are screws or rivets. However, fixation means <NUM> constituted by e.g. spot welding or gluing are also possible to use, depending on the application.

The actual operation of an electromechanical motor according to the basic consideration above is a very complex process, in which forces, inertia, frequencies, resonance properties etc. influences the final performance. In order to increase the understanding of the roles of the different quantities, a simplified model system can be analysed during the very first half cycle of electromechanical excitation. The first half cycle can be divided into three phases; a pre-loaded start condition, the initial snatch of the moved-body interaction portion from the body to be moved, and the very first free moving phase of the moved-body interaction portion.

<FIG> illustrates schematically the situation at the pre-loaded start condition. The moved-body interaction portion <NUM> is in mechanical contact with the body <NUM> to be moved with pre-load force F. This pre-load force is achieved by a certain displacement δsp of the fixation points relative to the body <NUM> to be moved and thereby relative to the top of the moved-body interaction portion <NUM>. The relation between displacement δsp and pre-load force F is expressed as: <MAT> where csp is the spring constant of said spring section.

<FIG> illustrates schematically the situation initial snatch of the moved-body interaction portion <NUM> from the body <NUM> to be moved. The pre-load force causes the stator, and in particular the spring section, to elastically deform. If such a pre-load force is momentarily released, the stator will start to vibrate with a motion that is composed of a set of natural resonance mode components. The dominating natural resonance mode in the direction of the pre-load is here denoted as the primary natural resonance mode fsp. In order to be able to remove the contact of the moved-body interaction portion <NUM>, the operation frequency fo of the voltages provided to the electromechanical volumes should at least be above the primary natural resonance frequency fsp of the entire electromechanical stator <NUM>. In other words, in one embodiment of an electromechanical motor, the voltage supply is arranged to supply the alternating voltages at an operation frequency fo at least above a primary natural resonance frequency fsp of the entire electromechanical stator.

The natural resonance frequencies of the electromechanical stator <NUM>, as for all other mechanical systems, depend on e.g. whether or not the part is pre-loaded or whether motion restrictions may occur. A free moving phase of the moved-body interaction portion resembles a free vibrating electromechanical stator with a prescribed initial condition. The primary natural resonance frequency for the entire electromechanical stator can be expressed as: <MAT> where meq is an equivalent lumped mass of the mass-spring representation of the electromechanical stator.

The analysis of the initial snatch can be brought further. If the operation frequency fo is used, the motion, represented by the distance in Z direction zip of the moved-body interaction portion <NUM>, can be expressed as: <MAT> where δip is an amplitude of the stroke of the tip of the moved-body interaction portion <NUM>.

The maximum acceleration then becomes: <MAT> and the time for performing a half cycle, which approximately is close to the time during which the moved-body interaction portion <NUM> is free from contact is: <MAT>.

<FIG> illustrates schematically the very first free moving phase of the moved-body interaction portion <NUM>. During this phase, the spring section <NUM> acts to push the moved-body interaction portion <NUM> back towards the body <NUM> to be moved. The distance of this pushing back can be denoted as Δδsp, and is controlled by the primary natural resonance frequency of the electromechanical stator. The distance can be approximated as: <MAT>.

The maximum acceleration then becomes: <MAT>.

The maximum push-back distance Δδmax is reached after approximately half a cycle, which gives: <MAT>.

By assuming that the maximum push-back distance Δδmax is small compared to δip: <MAT> where ξ is a small number, the expression (<NUM>) can be approximated by the two first terms of a Taylor series. Combining relations (<NUM>), (<NUM>) and (<NUM>), then gives an estimate of the operation frequency: <MAT>.

For achieving a good operation, the maximum push-back distance Δδmax should preferably be considerably smaller than the distance δip, preferably less than <NUM>% of the distance δip, i.e. ξ should preferably be less than <NUM>. The pre-load force F may in many typical applications be in the order of magnitude of 20N. A typical maximum distance δip between the moved-body interaction portion <NUM> and the body <NUM> to be moved may be in the range of <NUM> during the free moving phase. A typical equivalent lumped mass of an electromechanical stator may be in the range of <NUM>. Such assumptions would together point to an operation frequency of about <NUM>, which is fully feasible.

The acceleration asp of the electromechanical stator should also be considerably lower than the acceleration aip of the moved-body interaction portion <NUM>, preferably less than <NUM>% the acceleration aip.

It is also possible to express the ratio between the primary natural resonance frequency fsp and the preferred operation frequency fo: <MAT>.

If a maximum push-back distance Δδmax of <NUM> and a displacement δsp of <NUM> is assumed, this would require a frequency ratio of about <NUM>. These conditions will be rather different for different kinds of motors and applications and the preferred frequency ratio may therefore also vary substantially.

In a general context, however, the operational frequency fo should preferably exceed the primary natural resonance frequency fsp by at least a factor of <NUM>, more preferably by at least a factor of <NUM>, and most preferably by at least a factor of <NUM>.

The analysis above is made for the very first moments of an operation. However, the model involves an assumed "continuous" sinusoidal motion. This means that the initial velocity is "assumed" to be non-zero. Such imperfections in the model may give rise to e.g. minor delays or time shifts in the analysis. However, the conditions of a steady-state operation is assumed not to be very different from what has been used as the model above. The recovery of the pushing back distance may perhaps not lead to exactly the same starting position, but the main reasoning will anyway be valid at least within an order of magnitude.

The operation frequency fo is typically selected also to fit to the vibration properties of the vibration assembly, e.g. to be situated close to resonance frequencies of the vibration assembly. Suitable masses, spring constants and displacements of the spring section can then be found in order to fulfil the above estimations for an appropriate operation.

One advantage of using a continuous sheet of elastic material as a spring section is that spring constants of narrow material portions of beam shapes are relatively easy to estimate and predict. For instance, in the embodiments of <FIG>, the spring portions can be considered as being composed by serially connected straight beams and curved portions, having spring constant contributions that are relatively easy to estimate analytically and/or by simulations. In general, a longer path through the spring section between the connection points between the spring section and the support section and the attachment members between the actuator section and the support section gives a lower spring constant of the spring section. By using meandering shapes, very long paths can be achieved within a limited space. Likewise, if the width of the path is reduced, the spring constant will also decrease.

The use of a common continuous sheet of elastic material for all the active parts of the stator ensures a reliable geometric relation between the different parts of the stator. No uncontrolled displacements or bendings from additional mounting components influences the normal force application and the finally achieved normal force can be estimated very accurately from just the shape and elastic deformation distance of the spring section.

Many different detailed designs of the spring section are possible to use. <FIG> illustrates another embodiment of an electromechanical motor <NUM>. Here the meandering is provided in a direction perpendicular to the meanderings of <FIG>.

<FIG> illustrate other examples or embodiments of spring section patterns, using the ideas of utilizing curved narrow material paths cut out in the continuous sheet of elastic material through the spring section. <FIG> illustrates an electromechanical stator <NUM>, outside the scope of the present invention, having four spring sections <NUM>, extending perpendicular from the support section <NUM>. This can be thought of as a straightening out of the earlier presented curved spring shapes. The spring properties of such a design are very easy to calculate, using standard beam vibration models. However, this example requires that there is plenty of available space on both sides of the actuator section.

<FIG> illustrates a spring section <NUM> having two fixation points <NUM>, but only one connection <NUM> to the support section <NUM>. This ensures that the normal force is applied in the middle of the support section <NUM>, and may be advantageous in applications where any allowed tilting around an axis perpendicular to the motion direction has to be limited.

In <FIG>, one support section <NUM> is connected to two separated spring sections <NUM>, each of which having its own fixation point <NUM>. Here the path between the connections <NUM> and the fixation points has a basically spiral shape.

In <FIG>, the width at the bends <NUM> of the meandering shapes of the spring section <NUM> are made larger in order to strengthen the structure at points where fatigue sometimes may occur.

<FIG>, illustrates a spring section <NUM> where all bends have large radii of curvature. This avoids sharp corners, where crack initiation may be a problem.

<FIG> illustrates an embodiment having two support sections <NUM> on each side of the actuator section <NUM>. This makes it possible to adapt the spring force applied at the different support sections <NUM>, e.g. for compensating unevenly applied load forces on the moved-body interaction portion <NUM>.

<FIG> illustrates an embodiment with a single support section <NUM> enclosing the actuator section <NUM>.

<FIG> illustrates an embodiment where the respective spring sections <NUM> are provided at a side of the support structures in the direction X of the intended motion of the motor. This makes the total motor narrower, but may require more free space along the motor.

<FIG> illustrates an embodiment of an electromechanical stator <NUM> having its support section and spring section on only one side. This could e.g. be favourable in rotating motor applications. In this particular embodiment, the attachment members <NUM> are provided to act at the middle of the actuator section <NUM>, in order to minimize any tendencies for tilting the actuator section as a result of the applied normal force. The attachment members <NUM> are therefore in this particular embodiment shaped as slender beams <NUM>. <FIG> is a view from the bottom of <FIG>, showing how the attachment members <NUM> are given additional space for movements by provision of cavities <NUM>.

In <FIG>, the electromechanical stator from <FIG> is applied in an embodiment of a twin-stator design for a rotating electromechanical motor. The fixation points <NUM> are in this embodiment attached to the shaft <NUM> of the rotating electromechanical motor <NUM>. Such an attachment is arranged in such a way that the fixation points <NUM> are freely rotatable in relation to the shaft <NUM>, e.g. by some bearing arrangement, but locked for displacements along the shaft <NUM>.

As can be seen in the discussions above, also the equivalent lumped mass of the electromechanical stator plays a role in finding suitable frequencies and spring properties. For instance, if a suitable spring section design, giving a requested spring constant has been found, but other parameters tend to cause a high recommended operation frequency, the frequencies can be adapted by adapting the mass of the support section. Since the support section does not essentially contribute to the spring action, but its mass contributes to the equivalent lumped mass of the electromechanical stator, additional mass can be added to the support section without significantly change the spring constant.

Another way of "tuning" the available ranges of operation frequencies, when a certain spring section design is fixed, is to modify the elastic deformation of the spring section. With reference to <FIG>, fixation points of two electromechanical stators in a twin-design are held together by the fixation means <NUM>. Such a situation corresponds to a displacement of each fixation point by the distance D. If a lower normal force is requested, e.g. for reducing the lower end of recommended operation frequencies, the situation illustrated in Fig. 11B may be used. Here, a distance element <NUM>, such as a washer can be supported between the fixation points <NUM>. The displacement D of each fixation point <NUM> will thereby be reduced somewhat. In other words, by simply adapting the distance that the fixation points <NUM> are moved during mounting, an adapted normal force can be achieved. Distance elements <NUM> can easily be manufactured with a high degree of accuracy in thickness, which means that the applied normal force also can be tuned very accurately.

Similar situations for a single electromechanical stator mounted against e.g. a bearing arrangement <NUM> are depicted in <FIG>.

In alternative embodiments, also plastic deformations of the continuous sheet of elastic material can be utilized to modify the displacement of the fixation points. <FIG> illustrates an electromechanical motor <NUM> having a twin-stator design as described before in which the support sections <NUM> of each electromechanical stator <NUM> are plastically deformed before mounting. By this plastic deformation, the necessary displacement of the fixation points <NUM> can be adapted to the prevailing thickness of the body to be moved.

In such embodiment, one has to be particularly careful to control the displacement caused by the plastic deformation, since such manufacturing processes typically are not very accurate. Preferably, the continuous sheet of elastic material <NUM> of at least the spring section <NUM> is, in a state free from elastic deformation, still flat. This ensures that the spring constant properties are well defined.

<FIG> is a flow diagram illustrating steps of a method for operating an electromechanical motor. The electromechanical motor comprises an actuator section, a support section and a spring section. A continuous sheet of elastic material constitutes at least a part of the actuator section, at least a part of the support section and at least a part of the spring section. The actuator section comprises a vibration assembly in turn comprising at least one vibration body and a moved-body interaction portion. The vibration body comprises an electromechanical volume attached to a part of the continuous sheet of elastic material. The support section is attached between the actuator section and the spring section. The support section is connected with at least one fixation point via the spring section. The spring section is elastic, with a spring constant.

The method comprises the step S10, in which a normal force is provided in a vibration direction, transverse to the plane of the continuous sheet of elastic material, on the moved-body interaction portion. This normal force provision is performed in step S12 by displacing the fixation point in the vibration direction. In step S20, alternating voltages are applied to the electromechanical volume, causing the vibration body to perform bending vibrations in the vibration direction.

In a preferred realisation, the applied alternating voltages are tuned to an operation frequency above a lowest natural resonance frequency of the entire electromechanical stator.

Claim 1:
An electromechanical stator (<NUM>) comprising an actuator section (<NUM>), a support section (<NUM>), and a spring section (<NUM>);
wherein a continuous sheet of elastic material (<NUM>) constitutes at least a part of said actuator section (<NUM>), at least a part of said support section (<NUM>), and at least a part of said spring section (<NUM>);
said actuator section (<NUM>) comprising a vibration assembly (<NUM>) comprising at least one vibration body (<NUM>) and a moved-body interaction portion (<NUM>);
said vibration body (<NUM>) comprising an electromechanical volume (<NUM>) attached to a part of said continuous sheet of elastic material (<NUM>), wherein said vibration body (<NUM>) is adapted to cause bending vibrations, in a vibration direction (Z) transverse to the plane of said continuous sheet of elastic material (<NUM>), when alternating voltages are applied to said electromechanical volume (<NUM>);
said support section (<NUM>) being attached between said actuator section (<NUM>) and said spring section (<NUM>);
said support section (<NUM>) being connected with at least one fixation point (<NUM>) via said spring section (<NUM>);
wherein said spring section (<NUM>) is elastic, with a spring constant, regarding displacements, in said vibration direction (Z), of said fixation point (<NUM>) relative to a connection point (<NUM>) between said spring section (<NUM>) and said support section (<NUM>), thereby enabling provision of a normal force (F) in said vibration direction (Z) on said moved-body interaction portion (<NUM>) upon displacement of said fixation point (<NUM>) in said vibration direction (Z),
characterized in that
said continuous sheet of elastic material (<NUM>) of said spring section (<NUM>) has a pattern of cuts (<NUM>), providing at least one limited path (<NUM>) between connection points (<NUM>) to said support section (<NUM>) and said at least one fixation point (<NUM>).