WO2023244160A1

WO2023244160A1 - Drive elements for electromechanical motor

Info

Publication number: WO2023244160A1
Application number: PCT/SE2023/050605
Authority: WO
Inventors: Mats Bexell
Original assignee: Precibeo Ab
Priority date: 2022-06-17
Filing date: 2023-06-16
Publication date: 2023-12-21

Abstract

Disclosed is a drive element (10) for an electromechanical motor adapted for attachment to a drive element support mechanically connecting at least two drive elements. The drive element comprises at least two separate actuators (20) mechanically connected by a common contact portion (4) at one end. Each actuator is a separately controllable phase segment and comprises a monolithic multilayer structure adapted to be mechanically connected at the second end to the drive element support. The multilayer structure comprises alternating phase electrode layers (15) and earth electrode layers arranged in planes perpendicular to the longitudinal extension of the drive element.

Description

Title

Drive elements for electromechanical motor

Field of the invention

The present invention relates to a drive element for an electromechanical motor, an electromechanical motor comprising such drive element, and a method for manufacturing a drive element, according to the preambles of the independent claims.

Background

Using electrical fields to cause a mechanical deformation of various materials has been used in a variety of technical fields. The electrostrictive and piezoelectric effect has for instance been used to effect movement in miniature motors. For example, EP1310038B1 and EP2053669A1 describes an electromechanical walking actuator arrangement and method for driving such an arrangement. The drive elements and passive backing structure are comprised in a single monolithic multilayer unit. Within each drive element phase electrode layers and earth electrode layers are arranged alternately. The phase electrode layers all connect to a common electrode on the front side, and the earth electrode layers all connect to a common electrode on the back side.

The use of monolithic drive elements entails a complex and costly manufacturing process with high risk of having to discard the complete monolithic unit, including one or several drive elements, if one step in the manufacturing process is not up to the required standard.

Further, due to the mechanical strain in the materials in the drive element when actuated, material fatigue and cracks occur over time, which decreases the lifetime of the motor. In addition, known electromechanical walking actuators also consume high amounts of energy and generates high levels of heat, in order to produce the desired amount of force.

Thus, drive elements in known electromechanical motors usually utilize the active material in an ineffective way. This may lead to uneven motion of different drive elements as well as premature drive element failure.

The inventor of the present invention has thus identified a need for an improved drive element for an electromechanical motor. Summary

An object of the present invention is to provide a drive element for an electromechanical motor that has an increased life expectancy.

Another object of the present disclosure is to provide a more energy-efficient drive element for an electromechanical motor.

A further object of the present invention is to provide a drive element for an electromechanical motor that is less complicated and less costly to manufacture.

The above-mentioned objects are achieved by the present invention according to the independent claims. Preferred embodiments are set forth in the dependent claims.

In accordance with the present invention a drive element for an electromechanical motor has a longitudinal extension along an axis, a first end comprising a contact portion adapted for contact with an object to be moved in a main direction being essentially perpendicular to the longitudinal axis of the drive element. The drive element further has a second end adapted for attachment to a drive element support mechanically connecting at least two drive elements. The drive element comprises at least two separate actuators mechanically connected by a common contact portion at the first end. Each actuator is a separately controllable phase segment and comprises a monolithic multilayer structure adapted to be mechanically connected at the second end of the drive element support. The multilayer structure comprises alternating phase electrode layers and earth electrode layers arranged in planes essentially perpendicular to the longitudinal extension of the drive element.

In one aspect, the at least two separate actuators are arranged with a longitudinal gap between the separate actuators within the drive element, such that the the actuators can move completely separately from each other to cause bending or other movement of the drive element, as the actuators are not connected along the majority of the length of the actuators.

In another aspect, the at least two separate actuators are operationally connected to each other only by the common contact portion at the first end and by a drive element support, when the drive element is attached to the drive element support at the second end. Thus, the actuators can move completely separately from each other to cause bending or other movement of the drive element, as the actuators are not connected along the majority of the length of the actuators.

In contrast to the monolithic bimorphous elements forming a drive element in known prior art, a drive element for an electromechanical motor with two mechanically separate actuators as disclosed herein provides a motor with higher yield and more consistent performance, as well as an increased lifespan. In addition, such a motor provides increased force and stiffness, with less energy consumption and less heat generation. Further, the use of separate actuators provides a tunable stiffness. The resulting motor will thus have a smoother and more accurate walking motion, while at the same time being more energy efficient.

Further, a method of manufacturing a drive element for an electromechanical motor is disclosed, comprising the steps: manufacturing at least two separate actuators by arranging alternating phase electrode layers and earth electrode layers, thereafter arranging said actuators in pairs by attaching a common contact portion at a first end of the actuators to form a drive element.

Manufacturing the two actuators for a drive element before attaching them to a common contact portion or to a common backing structure, e.g. a drive element support, provides higher adaptability during manufacture, and allows for individual attention and quality control of variations in each actuator. The present disclosure will become apparent from the detailed description given below. The detailed description and specific examples disclose preferred embodiments of the disclosure by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the disclosure.

Hence, it is to be understood that the herein disclosed disclosure is not limited to the particular component parts of the device described or steps of the methods described since such device and method may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It should be noted that, as used in the specification and the appended claim, the articles "a", "an", "the", and "said" are intended to mean that there are one or more of the elements unless the context explicitly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings does not exclude other elements or steps.

Brief description of the drawings

Figures 1a-1d show various views of drive elements of known configuration. Figures 2a-2d show various views of one aspect of a drive element for a walking type electromechanical motor.

Figure 3 shows a drive element arrangement for a walking type electromechanical motor.

Figure 4 shows a walking type electromechanical motor.

Figure 5 illustrates the movement of drive elements in a walking type electromechanical motor.

Figure 6a and 6b illustrate different configurations of actuators in a drive element for a walking type electromechanical motor.

Figures 7a-7d show various views of another aspect of a drive element for a walking type electromechanical motor.

Detailed description

A walking type of electromechanical motor, also called a piezomotor, as disclosed herein comprises at least two drive elements, with contact portions arranged at a first end of each of the drive elements, and an object to be moved by the drive elements. The contact portions are adapted for contact with the object to be moved. The object to be moved is preferably arranged in a main direction being essentially perpendicular to a longitudinal extension of the drive element, as seen at least when the electromechanical motor is not in motion. The drive elements are made of piezoelectric material and adapted to produce a movement of the object to be moved in the main direction by “walking” along the object to be moved. An electromechanical motor may thus also preferably comprise electrical leads and electrodes arranged to apply a suitable electric field to the piezoelectric material. By applying a suitable voltage to the piezoelectric material via the electrode layers, electrical fields will be applied within different parts of the drive element and result in an expansion or contraction of the piezoelectric material between phase electrode layers and earth electrode layers. Due to the arrangement of the piezoelectric material within the drive element, the drive elements themselves will bend and/or contract or expand, which will cause movement of the contact portions, resulting in a walking motion along the object to be moved.

Figure 1a-d shows different views of the traditional configuration of a drive element 1 for an electromechanical motor, e.g. as disclosed in EP1310038B1 or US6798117B2. Such drive elements 1 are arranged within in a single monolithic multilayer unit comprising at least two, often four, drive elements and an integrated passive backing structure (not illustrated in the figures) supporting the drive elements. Each drive element comprises a bimorphous monolithic element in itself. Figure 1a shows a known drive element from a front view, wherein the drive element is adapted to achieve movement of an object to be moved in a main direction D. The drive element has a longitudinal extension along an axis A-A’ and a contact portion 4 arranged at a first end 2. The contact portion 4 is arranged to contact the object to be moved, which would be arranged above the illustrated drive element 1. A second end 3 of the drive element 1 is integrated with a backbone structure (not illustrated) wherein the drive element(s) of a walking actuator form a unitary monolithic unit together with the backbone. In motion, the bimorphous monolithic drive element 1, will bend and move such that the contact portion 4 will move the object to be moved in the direction D.

Figure 1b shows a side view of the drive element 1, viewed from the right side of Figure 1a. A phase electrode 6 is arranged vertically along each half of the drive element 1. Phase electrode layers 5 extend horizontally from each of the phase electrodes 6 into the drive element 1 , such that there will be two separate phase electrodes in a chosen horizontal plane of the drive element 1. This is best seen in Figure 1 c, which shows a top view of a cross-section of the drive element 1 taken along line B-B’ in Figure 1b. Thus, Figure 1c illustrates the surface area of two phase electrode layers 5 within a chosen horizontal plane of the drive element 1. Similarly, on the back side of the drive element 1, two earth electrodes 8 are arranged vertically along each half of the drive element 1. However, for the earth electrode a common earth electrode layer 7 is arranged across both halves of the drive leg, and extends horizontally into the drive element 1 from the earth electrodes 8. This is best seen in Figure 1 d, which shows a top view of a cross-section of the drive element 1 taken along line C-C’ in Figure 1b.

To achieve movement of the drive element a suitable voltage is applied to selected phase electrodes. This causes a shape change of the piezomaterial which results in bending and/or expansion/contraction of the drive element. In order to insulate the layers from each other, insulation areas 9 are arranged in the electrode areas such that e.g. the phase electrode layers do not risk contact with the earth electrode. The monolithic arrangement of this known drive element can lead to excessive mechanical strain of the material. The insulation areas 9 will in effect to some extent impede or interfere with the bending/elongation of the drive element. In addition, insulation areas 9' between two phase electrode layers 5 in a cross- sectional plane B-B’ (Figure 1c) are also subject to mechanical strain and lessen the effective bending/elongation caused by an applied electric field.

Figure 2a shows one aspect of a drive element for an electromechanical motor according to the present disclosure. Figure 7a shows another aspect of a drive element for an electromechanical motor according to the present disclosure. Unless otherwise detailed, the following applies to both the drive element of figures 2a-2d and the drive element of figures 7a-7d. The drive element 10 has a longitudinal extension along an axis A-A’ and a first end 2 comprising a contact portion 4. The contact portion 4 is adapted for contact with an object to be moved 30 (see Figures 3-5) in a main direction D being essentially perpendicular to the axis A-A’ of the drive element 10. The object to be moved 30 is often a shaft or other elongated object within the electromechanical motor. One example of an electromechanical motor comprising drive elements 10 are shown in Figure 4, which will be described below.

The drive element 10 is adapted for attachment to a drive element support 40 at the second end 3, located opposite the first end. The second end 3 is adapted to be mechanically connected to the drive element support 40 and thereby connects at least two drive elements 10 with each other, when assembled. This is shown in Figure 3, which will be detailed below.

In contrast to the known drive elements described above, the drive element 10 comprises at least two separate actuators 20. By “separate” is herein meant that the two actuators 20 are physically separate, and are made separately, before attachment to a common structure. After manufacture of the individual actuators, which will be further detailed later on, they are assembled into pairs, mechanically connected by a common contact portion 4 at the first end 2. Preferably, the two separate actuators 20 are operationally connected only by the common contact portion, i.e. the actuators can move completely separately from each other to cause bending or other movement of the drive element, as the actuators are not connected along the majority of the length of the actuators. Thus, in the assembled drive element 10 they are mechanically connected by the common contact portion 4 at the first end 2 and by the drive element support at the second end 3, and operationally separate along the length of the actuators.

Each of the actuators 20 are thus separately controllable phase segments, comprising a monolithic multilayer structure. The multilayer structure has alternating phase electrode layers 15 and earth electrode layers 17, which are arranged in a direction perpendicular to the longitudinal extension of the drive element 10. Each actuator 20 comprises at least one phase electrode layer 15 and at least one earth electrode layer 17. In Figures 2a, 2b, 7a and 7b the actuators comprise five phase electrode layers and five earth electrode layers, primarily for illustrative purposes, however any suitable number of electrode layers is conceivable, preferably between 10 and 150 of phase electrode layers and earth electrode layers in total, more preferably between 40 and 120 of phase electrode layers and earth electrode layers in total. The total number of electrode layers, i.e. both phase electrode layers 15 and earth electrode layers 17, is also related to the chosen distance between the individual electrode layers. The distance between the individual electrode layers may be between 10 pm and 100 pm, preferably between 15 pm and 60 pm. As an example, if the distance between the electrode layers is 20 pm, each actuator 20 may have approximately 75-100 electrode layers in total.

Figure 2b shows a side view of one aspect of the drive element 10, viewed from the right side of Figure 2a. The phase electrode layers 15 are shown in Figure 2c in a top view of the cross-sectional plane B-B’ of Figure 2b. Similarly, the earth electrode layers 17 are shown in Figure 2d in a top view of the cross-sectional plane C-C’ of Figure 2b. Figure 7a to 7d shows corresponding views of another aspect of a drive element 10. The main difference between the illustrated aspect of Figures 2a-2d and that of 7a-7d is in the extension of the electrode layer across the cross-section of the actuator, related to electrical insulation arrangements balanced with mechanical characteristics, as will be detailed below.

Referring to the aspect of Figures 2a and 2b, as can be seen, the phase electrode layers 15 and the earth electrode layers 17 all extend essentially to all the outer edges of the actuator 20, i.e. have a planar area essentially corresponding in size to an entire horizontal cross- sectional area of the actuator 20. In other words, the electrode layers 15, 17 extend over the majority of the cross-sectional area of the actuator in an electrode plane, and are also essentially equal in size. As can be seen by combining Figures 2a, 2b, 2c, and 2d it is clear that all outer edges of the planar area of the phase electrode layers 15 and the planar area of the earth electrode layers 17 are essentially aligned in a longitudinal direction within each actuator 20. Preferably, in this aspect, the electrode layers, both phase electrode layers 15 and earth electrode layers 17 constitute between 90 % and 100 %, more preferably between 97 % and 100 %, and even more preferably between 99 % and 100 % of the cross-sectional area of the actuator 20 in an electrode plane.

As seen in both Figures 2a-2d and 7a-7d, a phase electrode 16 is arranged vertically along each actuator 20, connected to the phase electrode layers 15. Similarly, on the opposite side of the actuator, an earth electrode 18 is arranged vertically along each actuator 20, connected to the earth electrode layers 17.

As illustrated in the drive element 10 of Figures 2a-2d, to avoid short-circuiting the different layers, insulation nodes 19 may be arranged between the phase electrode 16 and each earth electrode layer 17 on one side and between the earth electrode 18 and each phase electrode layer 15 on the other side. The insulation nodes 19 are preferably arranged on the outside of the actuator body, i.e. outside both piezomaterial and the electrode layers, such that the piezomaterial is allowed to expand or contract freely, and the electrode layers cover the majority of the cross-sectional area of the actuator in an electrode plane. Also, in the drive element of figures 7a-7d, a phase electrode 16 is arranged vertically along each actuator 20, connected to the phase electrode layers 15. Similarly, an earth electrode 18 is arranged vertically along each actuator 20 on the opposite side from the phase electrode 16. The earth electrode 18 is connected to the earth electrode layers 17. Notably, in this aspect, to avoid short-circuiting the different layers, a thin insulation region 25 is arranged at the three sides of the layer not connected to the respective vertical electrode 16, 18.

Thus, as an alternative to insulation nodes 19, the phase electrode layers 15 and the earth electrode layers 17 may be arranged with a continuous insulation region 25 along the perimeter on an electrode layer, at least at the edge opposing the respective connected electrode, and preferably also along the sides of the electrode layer, between the two opposing edges of the connected electrodes, as best seen in Figures 7c and 7d. Thus, in a phase electrode layer 15, the insulation region 25 insulates the phase electrode material from the earth electrode 18. Similarly, in an earth electrode layer 17, the insulation region 25 insulates the electrode layer material from the phase electrode 16.

Notably, at the same time, the phase electrode layers 15 and the earth electrode layers 17 extend over a majority of the cross-sectional area of the actuator in an electrode plane, and are also essentially equal in size. However, in this aspect, due to the insulation region 25 arranged at the perimeter on at least one side, and preferably three sides, the electrode layers, i.e. both phase electrode layers 15 and earth electrode layers 17 constitute between 60 % and 100 %, more preferably between 80 % and 100 %, of the cross-sectional area of the actuator 20 in an electrode plane.

From a mechanical point of view, it is an advantage to have the electrode layers extending as close to the perimeter of the actuator 20 as possible. This limits strain concentrations, which might lead to cracks and reduced lifetime. However, from an electrical point of view, it is necessary to have the electrodes properly covered (insulated) since the risk for electrical failure is high, especially in humid conditions. Therefore, in practice, actuators should be covered with some type of insulation, e.g. resin, glass or ceramic materials. Preferably the insulation region 25 should be as narrow as possible to avoid unnecessary restriction of actuator motion, but wide enough to protect the actuator from the environment. The insulation layer could either be applied after the actuator has been manufactured or in the actuator manufacturing process and co-sintered with the actuator, which saves some process steps. As described above, depending on the insulation layer thickness the electrode area may cover 60-95% of the cross-sectional area of the actuator. A well-insulated electrode will allow for high field strength levels. To reach similar strain values for soft and harder piezoceramics the electric field strain must be higher for hard materials. This can be achieved by either increasing the drive voltage level or reducing the electrode distance. The latter is often preferred since then the drive voltage can be kept at the same level, and may be achieved by making the different layers thinner than traditional arrangements.

In further aspects, not illustrated in the figures, to minimize effects of stress concentrations and at the same time avoid electrical failures, one may arrange only earth electrode layers 17 extending to the perimeter on all sides of the actuator 20, while arranging the phase electrode layers 18 with a thin insulation region 25 around three sides of the perimeter. In such an actuator, insulation nodes 19 are preferably arranged between the phase electrode 16 and each earth electrode layer 17 on one side of the actuator. This gives an electric field and mechanical strain gradient in the actuator which reduces stress concentrations and at the same time minimizes the risk for electrical failure.

Further, as can be seen in e.g. Figures 2a, 2c, 2d, 7a, 7c, and 7d, the two separate actuators 20 within a drive element 10 of any aspect disclosed herein are arranged with a longitudinal gap 21 within the drive element and between the separate actuators 20. The gap 21 is preferably arranged along the axis A-A’ of the drive element 10. This gap may be left empty, or be filled with e.g. a resin. The gap 21 may be anything from around a few micrometers to several millimetres wide. As mentioned, each actuator 20 is made separately, and thereafter combined in pairs to form a drive element 10. When used, they are thus mechanically connected at least at their second ends to the drive element support 40. Two exemplary configurations of drive elements 10 are illustrated in Figure 6a and 6b. As is understood from these figures, the dimensions, and thereby the bending characteristics, of the drive element 10 may be varied by arranging a smaller or larger gap 21 between the actuators 20. The advantages of such an arrangement are further detailed below.

Figure 3 illustrates a drive element arrangement 45 comprising any of the herein disclosed drive elements 10, mechanically connected to a drive element support 40 arranged to mechanically connect the at least two drive elements at the second ends 3 of the drive elements. Figure 3 also illustrates that the contact portion 4 of a drive element 10 is adapted for contact with an object to be moved 30. Notably, the arrangement is Figure 3 is in a resting position, i.e. the drive elements have not been activated by applying a drive voltage.

Figure 4 illustrates an electromechanical motor 50 comprising the above described drive elements 10. An object to be moved 30 is arranged in a main direction D being essentially perpendicular to the longitudinal extension of the at least two drive elements 10. A drive element support 40 is arranged to mechanically connect the at least two drive elements 10 at the second ends 3 of the drive elements. A walking type of electromechanical motor 50 as illustrated may also comprise a housing 47 and a roller unit 46 on the opposite side of the object to be moved 30, compared to the drive elements. The roller unit 46 may be arranged to support and guide the object to be moved 30.

In some aspects, drive element 10 is made by mechanically connecting two actuators 20 to each other, side by side as seen in Figure 3, by a common contact portion 4 at the first end. The drive elements 10 are thereafter attached to the drive element support 40, and optionally also via a resin or glue in the longitudinal gap 21 between the two actuators 20. A common arrangement comprises four drive elements on a drive element support 40.

Two coupled actuators can effect a bending movement by coordinated application of drive voltages over each actuator, e.g. such that the two coupled actuators expand differently in length. Figure 5 illustrates a sequence of events (a-d) in an arrangement comprising the disclosed drive elements 10 attached to a drive element support 40, wherein the drive elements are active and moving in motion along object to be moved 30. As the actuators 20 are coupled to each other in the drive element 10, the drive element 10 will bend in response to an applied voltage to each actuator 20, and a controlled movement of the contact portions 4 can be achieved, resulting in a walking motion along the object to be moved 30.

In the illustrated arrangement in Figure 5, the first and fourth drive element, as seen from left to right in the figure, are a first synchronous pair, and the second and third drive element are a second synchronous pair. In step (a) the first pair has just finished a movement in direction D and the second pair have just initiated contact with the object to be moved 30. In step (b) the second pair is moving the object to be moved 30, while the first pair has retracted and are in the process of bending back towards the left side to initiate another movement step (step (c)). Similarly, in step (d) the first pair is moving the object to be moved 30, while the second pair has retracted and are in the process of bending back towards the left side to initiate another movement step. This cycle is repeated as needed, and may also be reversed, for movement of the object to be moved in the opposite direction.

The disclosed arrangement of the actuators 20, wherein two separate actuators 20 form a drive element, and each actuator is a separately controllable phase segment, allows for more efficient use of the piezoelectric material in the drive element 10. In the disclosed configuration, wherein the planar area of each electrode plane extends over a majority of the cross-sectional area of the actuator in an electrode plane, very little of the cross-sectional area of the actuator in an electrode plane goes unused when actuating the actuator by applying an electric field. Further, it lessens mechanical strain on the actuator’s piezomaterial. By using as much as possible of the cross-sectional area of an actuator for actuating a bending movement, there is essentially no unaffected piezomaterial to impede or interfere with the bending of the actuator. The only insulating parts of the actuator, i.e. insulation nodes 19 or insulation regions 25, are arranged to minimize any effect on mechanical strain during movement. As a result, a lower electric field strength is needed to actuate bending/extension.

Drive elements based on separately produced and mounted actuators as disclosed herein provide a number of advantages in view of traditional drive elements in a piezomotor, as will be detailed further below. A higher yield and more consistent performance is achieved, as well as an increased lifespan. In addition, a motor with drive elements according to the present disclosure provide increased force, with less energy consumption and less heat generation. Further, the use of separate actuators provides a tuneable stiffness of a drive element.

The production of the actuators as separate units before assembly into a drive element presents the opportunity to quality check the characteristics of each actuator before assembly, one at a time. This means that if one actuator is found to not meet the production requirements, only that single actuator needs to be discarded, compared to a full monolithic unit including two, eight or more actuators, as in prior art. This leads to higher yield, as less material is discarded.

Further, by quality checking each separately produced actuator, it may be ensured that both actuators in a drive element have the same characteristics, in contrast to prior art, resulting in a higher quality drive element and motor.

For instance, in a drive element according to prior art, the slightest misalignment of the electrode layers 5 and 7 in Fig. 1c-d immediately results in that one of the actuators acquires a larger active electrode layer area than the other actuator in the same drive element. Since the two actuators are co-sintered, this means that one of the two actuators in the drive element will expand more than the other, given the same voltage, and that the drive element thereby will move longer and higher in one direction than the other. This leads to inconsistent force, step length and motion in the two directions of the motor.

However, by manufacturing the actuators separately, quality checking each actuator and matching pairs of actuators with the same characteristics, the actuators in the drive element will expand symmetrically, given the same voltage. The drive element will thus move equally long and high in both directions, resulting in consistent force, step length and motion in the two directions of the motor. The separate production of the actuators means that the two actuators are mounted separately in the drive element. Since each of the two actuators can move freely, the internal strain that is generated between the two co-sintered actuators in a monolithic unit according to prior art, is eliminated. This decreases the risk for material fatigue and cracks in the drive elements and increases the lifetime of the motor.

The production of the actuators separately, and the consequential elimination of the inner strain between the two actuators in the drive element, also means that each actuator can provide higher force, since no force is needed to overcome the inner strain between the two actuators.

Furthermore, the production of the actuators separately and the consequential elimination of the inner strain between the two actuators in the drive element, also means that the drive element needs less energy to perform each step. The motor according to the present disclosure therefore consumes less energy and generates less heat, since no energy is needed to overcome the inner strain between the two actuators.

Yet another effect of the production of the actuators separately is allowing freedom in placing two actuators at any chosen distance from each other within a drive element, depending on the needs for a particular drive element and motor. For instance, if a motor needs to be stiffer in the movement direction, the actuators are placed further apart from each other, with a larger gap between them, to increase the stiffness. For example, arranging a larger gap 21 between the actuators 20, as seen in Figure 6b compared to Figure 6a, will result in a stiffer drive element 10. This results in a motor with high stiffness for a small volume of active material.

Overall, the above advantages make it possible to achieve a motor with higher yield and more consistent performance, smoother and more accurate walking motion, a longer lifespan, and higher efficiency than known electromechanical motors, with good opportunities to further miniaturize such motors.

The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.

Claims

1. A drive element (10) for an electromechanical motor (50), said drive element (10) having a longitudinal extension along an axis (A-A’), said drive element (10) having a first end (2), said first end (2) comprising a contact portion (4) adapted for contact with an object to be moved (30) in a main direction (D) being essentially perpendicular to said axis (A-A’) of the drive element (10), said drive element (10) having a second end (3) adapted for attachment to a drive element support (40) mechanically connecting at least two drive elements (10), characterised in that said drive element (10) comprises at least two separate actuators (20) mechanically connected by a common contact portion (4) at the first end (2), each actuator (20) being separately controllable phase segments, each actuator (20) comprising a monolithic multilayer structure adapted to be mechanically connected at the second end (3) to said drive element support (40), said multilayer structure comprising alternating phase electrode layers (15) and earth electrode layers (17), said phase electrode layers (15) and said earth electrode layers (17) arranged in planes essentially perpendicular to the longitudinal extension of the drive element (10).

2. A drive element (10) according to claim 1 , wherein each phase electrode layer (15) and each earth electrode layer (17) has a planar area extending over a majority of the cross- sectional area of the actuator in an electrode plane, said cross-sectional area being essentially perpendicular to said axis (A-A’) of the drive element (10).

3. A drive element (10) according to any preceding claim, wherein said at least two separate actuators (20) are arranged with a longitudinal gap (21) between the separate actuators (20) within the drive element (10).

4. A drive element (10) according to any preceding claim, wherein the at least two separate actuators (20) are operationally connected to each other only by the common contact portion (4) at the first end (2) and by a drive element support (40), when the drive element (10) is attached to the drive element support (40) at the second end (3).

5. A drive element (10) according to any preceding claim, further comprising an earth electrode (18), and each phase electrode layer (15) comprising an insulation region (25), said insulation region (25) arranged along a perimeter of said phase electrode layer (15) to insulate said phase electrode layer (15) from said earth electrode (18).

6. A drive element (10) according to claim 5, further comprising a phase electrode (16), wherein each earth electrode layer (17) comprises an insulation region (25), said insulation region (25) arranged along a perimeter of each earth electrode layer (17) to insulate said earth electrode layer (17) from said phase electrode (16).

7. A drive element (10) according to claim 5 or 6, wherein said electrode layers (15, 17) each constitute between 60 % and 100 %, more preferably between 80 % and 100 %, of the cross-sectional area of the actuator (20) in an electrode plane.

8. A drive element (10) according to any of claims 1 to 4, comprising an earth electrode

(18), a phase electrode (16) and insulation nodes (19), wherein one set of said insulation nodes (19) are arranged to insulate between said phase electrode layers (15) and said earth electrode (18), said insulation nodes (19) being arranged outside a main body of the actuator (20).

9. A drive element (10) according to claim 5 or 8, wherein one set of said insulation nodes

(19) are arranged to insulate between said earth electrode layers (17) and said phase electrode (16), said insulation nodes (19) being arranged outside a main body of the actuator (20).

10. A drive element (10) according to any preceding claim, wherein the distance between individual electrode layers (15, 17) is between 10 pm and 100 pm, preferably between 15 pm and 60 pm.

11 . A drive element (10) according to any preceding claim, wherein an actuator (20) comprises between 10 and 150 electrode layers (15, 17) in total.

12. A drive element (10) according to any preceding claim, wherein all outer edges of the planar area of the phase electrode layers (15) and the planar area of the earth electrode layers (17) are essentially aligned in a longitudinal direction within each actuator (20).

13. A drive element (10) according to any preceding claim, wherein the planar area of each of the phase electrode layers (15) and the planar area of each of the earth electrode layers (17) are essentially equal in size at least within a common actuator (20).

14. A drive element (10) according to any preceding claim, wherein each phase electrode layer (15) and each earth electrode layer (17) has a planar area essentially corresponding in size to an entire cross-sectional area of the actuator (20), said cross- sectional area being essentially perpendicular to said axis (A-A’) of the drive element (10).

15. A drive element arrangement (45) comprising at least two drive elements (10) according to any preceding claim, and a drive element support (40) arranged to mechanically connect the at least two drive elements (10) at the second ends (3) of the drive elements (10). An electromechanical motor (50), comprising: at least two drive elements (10) according to any of claims 1 to 14, an object to be moved (30) in a main direction (D) being essentially perpendicular to said longitudinal extension of the at least two drive elements (10), a drive element support (40) arranged to mechanically connect the at least two drive elements (10) at the second ends (3) of the drive elements (3). Method for manufacturing a drive element for an electromechanical motor, said method comprising the steps: manufacturing at least two separate actuators by arranging alternating phase electrode layers and earth electrode layers within an actuator, thereafter arranging said actuators in pairs by attaching a common contact portion at a first end of the actuators to form a drive element. Method according to claim 17, further comprising the step of attaching at least two assembled drive elements to a drive element support to form a drive element arrangement. Method according to claim 17 or 18, wherein said two actuators in a drive element are arranged with a gap between said two actuators.