MULTILAYER ELECTROSTATIC ACTUATOR

Abstract

To provide a simply-structured multilayer electrostatic actuator that exhibits a sufficient stroke and a sufficient contraction force in a specific drive range, and rapidly hardens upon an attempt to widen the interval between electrodes beyond the drive range. A multilayer electrostatic actuator (1) is configured by a plurality of actuator parts (2a, 2b. 2c) each including: a first film (3a.sub.1, 3b.sub.1, 3c.sub.1) having a plurality of first connection regions (7a.sub.1, 7b.sub.1, 7c.sub.1) formed on one surface in a predetermined pattern; and a second film (3a.sub.2, 3b.sub.2, 3c.sub.2) connected to the first film via the first connection regions, and having a plurality of second connection regions (7a.sub.2, 7b.sub.2, 7c.sub.2) formed on a surface opposite to the first film in the identical pattern. The actuator parts are connected and layered via the second connection regions. On both the first film and the second film of one actuator part (2a, 2b. 2c), a non-connection region (15) is formed having a substantially fixed width between connection regions adjacent to each other as viewed in a layering direction (Z). The first connection regions and the second connection regions are arranged so as not to overlap each other as viewed in the layering direction. Axes of the patterns between two actuator parts (2a, 2b; 2b, 2c) connected intersect each other at a predetermined angle (θ, except θ =0°) as viewed in the layering direction. When the multilayer electrostatic actuator is pulled in the layering direction due to an external force, the non-connection region, in particular mainly the non-connection region of the second film, is bending-deformed to separate the first film and the second film, resulting in the multilayer electrostatic actuator extending in the layering direction. Further pulling makes the non-connection region tensile-deformed and hardened. When a voltage is applied, the multilayer electrostatic actuator contracts in the layering direction due to the electrostatic attractive force.

Claims

1. A multilayer electrostatic actuator including a plurality of actuator parts layered, the actuator parts each comprising: a first film having a plurality of first connection regions formed on one surface in a pattern predetermined; and a second film connected to the first film via the first connection regions, and having a plurality of second connection regions formed on a surface opposite to the first film in a pattern identical to the pattern of the first connection regions, wherein on both the first film and the second film, a non-connection region is formed having a substantially fixed width between connection regions adjacent to each other as viewed in a layering direction (Z), the first connection regions and the second connection regions of each of the actuator parts are arranged so as not to overlap each other as viewed in the layering direction, two actuator parts overlapping each other among the actuator parts are connected via the second connection regions, and the two actuator parts connected are layered such that axes of the patterns between the two actuator parts intersect each other at an angle (θ, except θ = 0°) predetermined as viewed in the layering direction.

2. The multilayer electrostatic actuator according to claim 1, wherein in each of the actuator parts, axes of the pattern of the first connection regions are parallel to each other, and axes of the pattern of the second connection regions are parallel to each other.

3. The multilayer electrostatic actuator according to claim 1, wherein in each of the actuator parts, axes of the pattern of the second connection regions are parallel to axes of the pattern of the first connection regions.

4. The multilayer electrostatic actuator according to claim 1, wherein the patterns of the first connection regions and the second connection regions both form linear shapes having a substantially uniform width and arranged at equal intervals.

5. The multilayer electrostatic actuator according to claim 1, wherein in each of the actuator parts, one of the first connection regions is positioned at a center of the non-connection region between two of the second connection regions as viewed in the layering direction.

6. The multilayer electrostatic actuator according to claim 1, wherein when a plane formed by the two actuator parts layered is viewed in the layering direction, axes of the pattern of the first connection regions (7a.sub.1; 7b.sub.1) in the actuator part (2a; 2b) in an upper layer intersect axes of the pattern of the second connection regions (7b.sub.2; 7c.sub.2) in the actuator part (2b; 2c) in a lower layer at at least one point.

7. The multilayer electrostatic actuator according to claim 6, wherein the patterns of the first connection regions and the second connection regions both form linear shapes having a substantially uniform width (d) and arranged at equal intervals, and given that a length, on the plane as viewed in the layering direction, of the axes of the pattern of one of the first connection regions of the actuator part in the upper layer and the second connection regions of the actuator part in the lower layer is L, and a width between the non-connection regions in the one connection regions as viewed in the layering direction is 2 × ℓ + d, the angle θ [rad] of intersection of the axes of the patterns between the two actuator parts connected as viewed in the layering direction satisfies $\begin{array}{cc}\arctan \left(\frac{2\times l+d}{L}\right)<\left|\theta \right|\le \frac{\pi }{2}.& \text{­­­[Formula 3]}\end{array}$ .

8. The multilayer electrostatic actuator according to claim 1, wherein when the multilayer electrostatic actuator extends: the first film and the second film in each of the actuator parts are separated from each other to form a space (13) in the non-connection region of the first film and the second film; and the first film of the actuator part in an upper layer and the second film of the actuator part in a lower layer are separated from each other to form a space (11) in the non-connection region of the first film and the second film, the two spaces (11, 13) are in fluid communication with outside, and fluid is allowed to flow in and out between the spaces and outside when the multilayer electrostatic actuator extends and contracts.

9. The multilayer electrostatic actuator according to claim 1, wherein a planar shape of the actuator parts is a quadrangle, and the two actuator parts overlapping each other are layered at the angle of intersection predetermined of 90°.

10. The multilayer electrostatic actuator according to claim 1, wherein the first film includes a three-layer structure of an insulating layer (23), a conductive layer (21), and an insulating layer (23), the second film is configured by an insulating layer, the second film has, as viewed in the layering direction, a first connection surface portion (8.sub.1) connected to the first film via the first connection regions, a second connection surface portion (8.sub.2) connected to the first film of the actuator part on an upper side in the layering direction via the second connection regions, and a hinge portion (15) in which neither the first connection regions nor the second connection regions are formed, when the multilayer electrostatic actuator is pulled in the layering direction due to an external force, the hinge portion is elastically deformed to separate the first film and the second film, and the multilayer electrostatic actuator extends in the layering direction, and when a voltage is applied between the first films of the two actuator parts layered, the two first films are attracted to each other due to an electrostatic attractive force, and the multilayer electrostatic actuator contracts in the layering direction.

11. The multilayer electrostatic actuator according to claim 1, wherein both the first film and the second film include a three-layer structure of an insulating layer (23), a conductive layer (21), and an insulating layer (23), the second film has a first connection surface portion (8.sub.1) connected to the first film via the first connection regions, a second connection surface portion (8.sub.2) connected to the first film of the actuator part on an upper side in the layering direction via the second connection regions, and a hinge portion (15) in which neither the first connection regions nor the second connection regions are formed, when the multilayer electrostatic actuator is pulled in the layering direction due to an external force, the hinge portion is elastically deformed to separate the first film and the second film, and the multilayer electrostatic actuator extends in the layering direction, and when a voltage is applied between the first film and the second film, the two films are attracted to each other due to an electrostatic attractive force, and the multilayer electrostatic actuator contracts in the layering direction.

12. The multilayer electrostatic actuator according to claim 11, wherein the first film and the second film have an elongated ribbon shape, the multilayer electrostatic actuator has a paper spring structure in which two first films and two second films are bent in a zigzag shape and alternately folded such that longitudinal directions of the first films and the second films intersect each other at 90° as viewed in the layering direction, on a plane where the two first films and the two second films overlap each other as viewed in the layering direction, a plurality of the actuator parts layered are formed, and a bent portion formed outside the plane constitutes an outer hinge portion (17), and the first films or the second films of the actuator parts in different layers are integrated with each other by the outer hinge portion.

13. The multilayer electrostatic actuator according to claim 11, wherein the first film and the second film have an elongated ribbon shape, the multilayer electrostatic actuator has a flat spiral wound structure in which two first films and two second films are wound in one direction from a center, on a plane where the two first films and the two second films overlap each other as viewed in the layering direction, a plurality of the actuator parts layered are formed, and a bent portion formed outside the plane constitutes an outer hinge portion (17), and the first films or the second films of the actuator parts in different layers are integrated with each other by the outer hinge portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0073] FIG. 1 is a perspective view illustrating the basic structure of a multilayer electrostatic actuator according to the present embodiment.

[0074] FIG. 2 is an exploded perspective view illustrating a portion of the basic structure of the actuator part illustrated in FIG. 1.

[0075] FIG. 3 is a cross-sectional view illustrating the layered structure of the films of the actuator part illustrated in FIG. 2.

[0076] FIG. 4 is an enlarged front view illustrating a portion of the basic structure of the actuator part illustrated in FIG. 1.

[0077] FIG. 5 is an enlarged side view illustrating a portion of the basic structure of the actuator part illustrated in FIG. 1.

[0078] FIG. 6 is a cross-sectional view illustrating the actuator part in the extended state of the multilayer electrostatic actuator illustrated in FIG. 1.

[0079] FIG. 7 is a graph illustrating the relationship between the resultant force of the electrostatic force and the spring force of the multilayer electrostatic actuator and the generated force of the electrode layer portion according to the present embodiment.

[0080] FIGS. 7-1 is an explanatory diagram for explaining the overlapping state of two actuator parts of the multilayer electrostatic actuator according to another embodiment, where (a) is a view as viewed in the layering direction, and (b) is a cross-sectional view taken along VII-VII in (a).

[0081] FIGS. 7-2 is an explanatory diagram for explaining the intersection condition for the connection regions in the multilayer electrostatic actuator illustrated in FIGS. 7-1.

[0082] FIG. 8 is a perspective view illustrating a multilayer electrostatic actuator created with a bent structure.

[0083] FIG. 9 is a perspective view illustrating a multilayer electrostatic actuator created with a wound structure.

DESCRIPTION OF EMBODIMENTS

[0084] Hereinafter, the configurations, manners of operation, and effects of the multilayer electrostatic actuator according to the present embodiment will be described in detail with reference to the embodiments illustrated in FIGS. 1 to 9. In the following description, first, the basic structure of the multilayer electrostatic actuator according to the present embodiment will be described, and next, components of the multilayer electrostatic actuator will be described in detail. Then, the manners of operation of the multilayer electrostatic actuator will be described, and further, the relationship between the generated force of the multilayer electrostatic actuator and the resultant force of the electrostatic force and the spring force will be mentioned. Next, two types of application examples of multilayer electrostatic actuators having a function of connecting electrodes of different layers will be described, and effects of the multilayer electrostatic actuators will be mentioned. Finally, other embodiments of multilayer electrostatic actuators that partially differ in configuration will be briefly described.

First Embodiment

1) Basic Structure of Multilayer Electrostatic Actuator

[0085] FIG. 1 is a perspective view illustrating the basic structure of a multilayer electrostatic actuator according to the first embodiment, and FIG. 2 is an exploded perspective view illustrating a portion of the basic structure of the actuator part of the multilayer electrostatic actuator illustrated in FIG. 1. As illustrated in FIG. 1, the multilayer electrostatic actuator 1 includes a plurality of actuator parts 2a, 2b. 2c...., 2n (hereinafter may be referred to as the “actuator part 2”) layered and sandwiched between end members 5a, 5b located on the upper and lower surfaces in the layering direction Z. Each of the actuator parts 2a, 2b, 2c has a planar shape that is quadrangular as viewed in the layering direction Z. As illustrated in FIG. 2, the actuator parts 2a. 2b, 2c respectively include first films 3a.sub.1, 3b.sub.1, 3c.sub.1 having a plurality of first connection regions 7a.sub.1, 7b.sub.1, 7c.sub.1 formed on one surface in a predetermined pattern, and second films 3a.sub.2, 3b.sub.2, 3c.sub.2 connected to the first films 3a.sub.1, 3b.sub.1, 3c.sub.1 via the first connection regions 7a.sub.1, 7b.sub.1, 7c.sub.1. The second films 3a.sub.2, 3b.sub.2, 3c.sub.2 respectively have a plurality of second connection regions 7a.sub.2, 7b.sub.2, 7c.sub.2 formed on the surface opposite to the first films 3a.sub.1, 3b.sub.1, 3c.sub.1 in a pattern identical to the pattern of the first connection regions 7a.sub.1, 7b.sub.1, 7c.sub.1. Two actuator parts 2a, 2b; 2b, 2c overlapping each other are respectively connected via the second connection regions 7b.sub.2;7c.sub.2, and the actuator part 2a is connected to the end member 5a located on the uppermost surface in the layering direction Z via the second connection regions 7a.sub.2.

[0086] Here, the first connection regions 7a.sub.1 are formed in linear shapes having a uniform width, and the plurality of first connection regions 7a.sub.1 are arranged on the first film 3a.sub.1 in parallel to each other at equal intervals. Similarly, the first connection regions 7b.sub.1 are also formed in linear shapes having a uniform width, and the plurality of first connection regions 7b.sub.1 are arranged on the first film 3b.sub.1 in parallel to each other at equal intervals. The first connection regions 7c.sub.1 are also formed in linear shapes having a uniform width, and the plurality of first connection regions 7c.sub.1 are arranged on the first film 3c.sub.1 in parallel to each other at equal intervals. In addition, the second connection regions 7a.sub.2, 7b.sub.2, 7c.sub.2 are formed in the linear pattern identical to the linear pattern of the first connection regions 7a.sub.1, 7b.sub.1, 7c.sub.1, respectively, and the plurality of second connection regions 7a.sub.2, 7b.sub.2, 7c.sub.2 are arranged on the second films 3a.sub.2, 3b.sub.2, 3c.sub.2 in parallel to each other at equal intervals. The linear pattern of the plurality of first connection regions 7a.sub.1 and the linear pattern of the plurality of second connection regions 7a.sub.2 are arranged so as not to overlap each other as viewed in the layering direction Z. The connection regions 7b. 7c are also arranged similarly. Therefore, on both the first films 3a.sub.1, 3b.sub.1, 3c.sub.1 and the second films 3a.sub.2, 3b.sub.2, 3c.sub.2, a non-connection region 15 is formed having a linear shape and a substantially fixed width at the center between connection regions adjacent to each other as viewed in the layering direction Z.

[0087] The actuator parts 2a, 2b, 2c having such a configuration are layered at an intersection angle θ of 90°. Consequently, in the multilayer electrostatic actuator 1, as illustrated in FIG. 1. the actuator part 2a of the first stage is provided under the end member 5a placed on the uppermost surface in the layering direction Z, and the actuator part 2b of the second stage is provided under the actuator part 2a with an angle difference of 90°. Similarly, the actuator parts 2c to 2n of the third to n-th stages are sequentially provided with an angle difference of 90°, and the end member 5b is placed on the lowermost surface in the layering direction Z, whereby the multilayer electrostatic actuator 1 is formed.

[0088] Here, the term “having a substantially fixed width” as used in this context in the present specification is intended to mean not only that the width of the non-connection region formed between connection regions is fixed as viewed in the layering direction Z, but also that the width can fluctuate in the range of about ±5 to 10% for manufacturing or other purposes. Although the first embodiment describes the case where the intersection angle θ is 90° as an example, the present invention is not limited thereto. For example, it is intended to include any angle other than 0° such as 60° or 72° (strictly, the acute angle portion between axes satisfies 0° < θ ≤ 90° (including a right angle)).

2) Components of Multilayer Electrostatic Actuator

<Film>

[0089] FIG. 3 is a cross-sectional view illustrating the layered structure of the films of the actuator part illustrated in FIG. 2. FIG. 3a illustrates the layered structure of the first films 3a.sub.1, 3b.sub.1, 3c.sub.1 (hereinafter referred to as the “conductive film p”) of the actuator parts 2a, 2b, 2c, and FIG. 3b illustrates the layered structure of the second films 3a.sub.2, 3b.sub.2, 3c.sub.2 (hereinafter referred to as the “insulating film Q”).

[0090] The conductive film p has a three-layer film structure including a conductive layer 21 at the center and insulating layers 23 on the front and back surfaces thereof, for example. The conductive layer 21 can be exemplified by a metal film such as copper (Cu) or aluminum (Al), a conductive polymer, or a conductive carbon allotrope (or a conductive mixture mainly composed of carbon). The insulating layer 23 can be exemplified by, but is not limited to, an insulating polymer film such as polyethylene terephthalate (PET), Kapton, parylene (registered trademark), a silicon-based material, or a carbon-based material. Here, given that the thickness of the conductive layer 21 is t.sub.21 and the thickness of the insulating layer 23 is t.sub.23, the thickness t of the conductive film p is t = t.sub.21 + 2 × t.sub.23. The thickness t of the conductive film p is, for example, several micrometers. Note that the three-layer film structure of the conductive film p is merely an example. In another example, the conductive layer 21 may have a multilayer structure made of dissimilar conductors having a plurality of different electrical conductivities and/or Young’s moduli, and the insulating layer 23 may have a multilayer structure made of dissimilar insulators having a plurality of different electrical resistivities and/or Young’s moduli.

[0091] On the other hand, the insulating film Q does not have any conductive layer 21. and consists of an insulating layer 23′. The insulating layer 23′ can be exemplified by, but is not limited to, an insulating polymer film such as polyethylene terephthalate (PET), Kapton, parylene (registered trademark), a silicon-based material, or a carbon-based material. In addition, the insulating layer 23′ may have a single-layer structure made of a single material, or may have a multilayer structure made of dissimilar insulators having a plurality of different electrical resistivities and/or Young’s moduli. Here, given that the thickness of the insulating layer 23′ is t.sub.23′, the thickness t′ of the insulating film Q is t′ = t.sub.23′. The thickness t′ of the insulating film Q is, for example, several micrometers.

<Connection Portion>

[0092] FIG. 4 is an enlarged front view illustrating a portion of the basic structure of the actuator parts 2a. 2b, 2c illustrated in FIG. 1, and FIG. 5 is a corresponding side view. Both drawings indicate a state in which an external force acts between the two end members 5a, 5b (FIG. 1) to separate the end members 5a, 5b in the layering direction Z. and the interval between the first films 3a.sub.1, 3b.sub.1, 3c.sub.1 and the second films 3a.sub.2, 3b.sub.2, 3c.sub.2 is extended. Because the first connection regions and the second connection regions (hereinafter may be referred to as the “connection region 7”) of each actuator part are separated from each other, a space 11, 13 is formed in the non-connection region 15 formed between the connection regions 7, 7 between upper and lower ones of the first films and second films layered.

[0093] More specifically, the plurality of first connection regions 7a.sub.1 of the actuator part 2a connect the first film 3a.sub.1 and the second film 3a.sub.2, and the space 13 is formed between adjacent first connection regions 7a.sub.1, 7a.sub.1 (FIG. 4). The plurality of second connection regions 7a.sub.2 connect the second film 3a.sub.2 and the end member 5a on the uppermost surface in the layering direction Z. and the space 11 is formed between adjacent second connection regions 7a.sub.2, 7a.sub.2. The first connection regions 7a.sub.1 are arranged so as not to overlap the second connection regions 7a.sub.2 as viewed in the layering direction Z. Specifically, the first connection regions 7a.sub.1 and the second connection regions 7a.sub.2 have linear shapes or band shapes extending in the depth direction Y and are arranged at equal intervals in the width direction X, and the first connection regions 7a.sub.1 and the second connection regions 7a.sub.2 are shifted by half a pitch in the width direction X so as to be positioned at the center of the space between counterpart connection regions. Similarly, the plurality of first connection regions 7c.sub.1 of the actuator part 2c connect the first film 3c.sub.1 and the second film 3c.sub.2, and the space 13 is formed between adjacent first connection regions 7c.sub.1, 7c.sub.1 (FIG. 4). The plurality of second connection regions 7c.sub.2 connect the second film 3c.sub.2 and the first film 3b.sub.1 of the actuator part 2b on the upper side in the layering direction Z, and the space 11 is formed between adjacent second connection regions 7c.sub.2, 7c.sub.2.

[0094] The plurality of first connection regions 7b.sub.1 of the actuator part 2b connect the first film 3b.sub.1 and the second film 3b.sub.2, and the space 13 is formed between adjacent first connection regions 7b.sub.1, 7b.sub.1 (FIG. 5). The second connection region 7b.sub.2 connect the second film 3b.sub.2 of the actuator part 2b and the first film 3a.sub.1 of the actuator part 2a, and the space 11 is formed between adjacent second connection regions 7b.sub.2, 7b.sub.2. The first connection regions 7b.sub.1 are arranged so as not to overlap the second connection regions 7b.sub.2 as viewed in the layering direction Z. In addition, the first connection regions 7b.sub.1 and the second connection regions 7b.sub.2 have linear shapes or band shapes extending in the width direction X and are arranged at equal intervals in the depth direction Y, and the first connection regions 7b.sub.1 and the second connection regions 7b.sub.2 are shifted by half a pitch in the depth direction Y so as to be positioned at the center of the space between counterpart connection regions.

[0095] An example of the material for connecting the first film and the second film in the connection region 7 is an adhesive, which is applied with high accuracy so as to have a constant application thickness and a predetermined pattern using a method such as relief printing, offset printing, stencil printing, or inkjet printing to form an adhesive portion. Alternatively, a chemical bonding layer may be formed on the insulating layer 23 or 23′ (FIG. 3) through chemical treatment such as surface treatment. In the case of forming an adhesive portion, the two films 3a.sub.1, 3a.sub.2 are bonded to each other via the adhesive. In the case of forming a bonding layer through chemical treatment, the two films 3a.sub.1, 3a.sub.2 are covalently bonded to each other. Other methods such as welding the insulating layer 23 or 23′ can be used without limitation to form the connection region as long as the above-described coupling pattern can be formed.

<Hinge Portion>

[0096] As described above with reference to FIGS. 4 and 5, because the second film 3a.sub.2 is connected at its upper and lower surfaces to the first connection regions 7a.sub.1 and the second connection regions 7a.sub.2, respectively, the portions (hereinafter referred to as the “connection surface portions 8.sub.1, 8.sub.2” (FIG. 6)) of the second film 3a.sub.2 corresponding to the first connection regions 7a.sub.1 and the second connection regions 7a.sub.2 have higher rigidity than the portions of the second film 3a.sub.2 corresponding to the other regions (non-connection regions that do not contribute to connection, hereinafter referred to as the non-connection region 15). Similarly, the connection surface portions 8.sub.1, 8.sub.2 of the second film 3b.sub.2 corresponding to the first connection regions 7b.sub.1 and the second connection regions 7b.sub.2 have higher rigidity than the non-connection region 15 of the second film 3b.sub.2.

[0097] When a tensile force (external force) in a direction in which the two end members 5a, 5b (FIG. 1) are separated is applied in the layering direction Z, the non-connection regions 15 of the second film 3a.sub.2 of the actuator part 2a and the second film 3b.sub.2 of the actuator part 2b are elastically deformed, and the intervals 3a.sub.1-3a.sub.2, 3b.sub.2-3a.sub.1, 3b.sub.1-3b.sub.2 between the first film and the second film are widened (FIGS. 4 and 5), resulting in the multilayer electrostatic actuator 1 extending in the layering direction Z (FIG. 1). A portion of the second film 3a.sub.2, 3b.sub.2 corresponding to the non-connection region 15 is defined as a “hinge portion 15”.

[0098] When a voltage is applied between the first film 3a.sub.1 of the actuator part 2a and the first film 3b.sub.1 of the actuator part 2b, the interval between the first films 3a.sub.1, 3b.sub.1 returns to the initial state (described later) due to the electrostatic attractive force caused by the applied voltage, and the interval between the first films 3a.sub.1, 3b.sub.1 is narrowed. The gap between the other first films 3b.sub.1, 3c.sub.1 is similarly narrowed due to the electrostatic attractive force, resulting in the multilayer electrostatic actuator 1 contracting in the layering direction Z.

[0099] The first film 3a.sub.1 of the actuator part 2a is connected at its upper surface to the second film 3a.sub.2 in the first connection regions 7a.sub.1 and connected at its lower surface to the second film 3b.sub.2 in the second connection regions 7b.sub.2. Because the first connection regions 7a.sub.1 extend in the depth direction Y and the second connection regions 7b.sub.2 extend in the width direction X, the second connection regions 7b.sub.2 act as ribs with respect to the deformation of the hinge portion 15 extending in the depth direction Y of the first film 3a.sub.1 of the actuator part 2a. Therefore, the first film 3a.sub.1 of the actuator part 2a has higher rigidity than the second film 3a.sub.2. Thus, when a tensile force (external force) is applied to the multilayer electrostatic actuator 1 in the layering direction Z. the hinge portion 15 of each of the second film 3a.sub.2 of the actuator part 2a and the second film 3b.sub.2 of the actuator part 2b is elastically deformed (bent and extended), but the elastic deformation of the first film 3a.sub.1 of the actuator part 2a is suppressed due to the above-described structure.

[0100] In the case where the deformation of the first film 3a.sub.1, 3b.sub.1 is suppressed and only the hinge portion 15 of the second film 3a.sub.2, 3b.sub.2 is deformed, the movement in the width direction X and the depth direction Y at the boundary position O (FIG. 6) between the hinge portion 15 and the connection surface portion 8.sub.1, 8.sub.2 on the second film 3a.sub.2, 3b.sub.2 is restrained. When the hinge portion 15 is deformed under such a restraint condition,the area near the boundary position O of the second film 3a.sub.2, 3b.sub.2 is mainly shear-deformed or bending-deformed so that the hinge portion 15 behaves like a soft spring: however, when an external force is applied in an attempt to cause further deformation, the hinge portion 15 is inclined in the layering direction Z, and the hinge portion 15 is tensile-deformed to behave like a hard spring. For this reason, in the small deformation range in which the multilayer electrostatic actuator 1 starts to extend in the layering direction Z from the initial state before external force application, the hinge portion 15 is soft, and the gap between the first films 3a.sub.1, 3b.sub.1 is likely to be widened in response to the external force. On the other hand, upon an additional external force applied in an attempt to cause further deformation, the hinge portion 15 rapidly becomes hard, which makes the gap between the first films 3a.sub.1, 3b.sub.1 less likely to be widened rapidly.

[0101] In other words, the spring constant of the hinge portion 15 of each actuator part 2a, 2b is small in the small deformation range of the multilayer electrostatic actuator 1 so that the actuator part 2a. 2b is softly deformed, whereas an attempt to cause further deformation beyond the small deformation range results in a rapid increase in the spring constant of the second film 3a.sub.2, 3b.sub.2, which makes each actuator part 2a, 2b less likely to be deformed rapidly. That is, the multilayer electrostatic actuator 1 has nonlinear spring characteristics in each actuator part 2a, 2b, which makes it possible to suppress excessive extension of the distance between films, in particular the distance between the first films 3a.sub.1, 3b.sub.1, and to obtain a sufficient electrostatic attractive force.

[0102] For the above reason, when a tensile force (external force) is applied to the multilayer electrostatic actuator 1 in the layering direction Z, the second film 3a.sub.2, 3b.sub.2 is elastically deformed in the actuator part 2a, 2b, and the multilayer electrostatic actuator 1 is put into the extended state. At this time, the deformation of the first film 3a.sub.1 is suppressed. When a voltage is applied to the multilayer electrostatic actuator 1 in the extended state, an electrostatic attractive force acts between the first film 3a.sub.1 of the actuator part 2a and the first film 3b.sub.1 of the actuator part 2b, and the interval between the first films 3a.sub.1, 3b.sub.1 is narrowed. As a result, the multilayer electrostatic actuator 1 contracts in the layering direction Z. Conversely, when the voltage is turned to zero, the non-connection region 15 of each of the second film 3a.sub.2 of the actuator part 2a and the second film 3b.sub.2 of the actuator part 2b is elastically deformed due to the external force, and the intervals 3a.sub.1-3a.sub.2, 3b.sub.2-3a.sub.1, 3b.sub.1-3b.sub.2 between the first film and the second film are widened, resulting in the multilayer electrostatic actuator 1 extending in the layering direction Z. Thus, the multilayer electrostatic actuator 1 can be extended and contracted by turning on/off the applied voltage.

<Space>

[0103] When a tensile force (external force) in the layering direction Z is applied to the multilayer electrostatic actuator 1 and the multilayer electrostatic actuator 1 is put into the extended state, the second film 3a.sub.2, 3b.sub.2 undergoes an increase in the space 11 with respect to the upper layer (the end member 5a on the uppermost surface in the layering direction Z and the first film 3a.sub.1 of the actuator part 2a, respectively) and an increase in the space 13 with respect to the lower layer (first film 3a.sub.1, 3b.sub.1, respectively) (FIGS. 4 and 5). These spaces 11, 13 are in fluid communication with outside in order to secure a sufficient amount of extension and contraction without hindering the extension and contraction operation of the multilayer electrostatic actuator 1 described below, and function as an insulating fluid portion through which an insulating fluid passes. In addition, the opening areas of these spaces 11 and 13 vary depending on the difference between the extension and contraction of the actuator part 2a, 2b. That is, when a tensile force (external force) in the layering direction Z is applied, mainly the second film is elastically deformed, and the interval between first films is separated, resulting in an increase in the opening area of the space 11, 13; whereas when a voltage is applied between electrode layers to cause an electrostatic attractive force, the interval between first films is narrowed, resulting in a decrease in the opening area of the space 11, 13.

3) Manner of Operation of Multilayer Electrostatic Actuator

[0104] In the multilayer electrostatic actuator 1 having the above configuration, the extension/contraction state varies depending on whether a tensile force (external force) is applied in the layering direction Z and whether a voltage is applied between first films.

<Initial State (Contracted State)>

[0105] In the initial state or when a voltage is applied between first films after application of a tensile force (external force) in the layering direction Z and an electrostatic attractive force acts and balances, the hinge portion 15 is not deformed, and the first film 3a.sub.1 and the second film 3a.sub.2 are in a planar state. At this time, the distance u from the conductive layer 21 of the first film 3a.sub.1 to the conductive layer 21 of the first film 3b.sub.1 (FIG. 3) is u.sub.initial = 2 × t.sub.23 + t.sub.23′ (not illustrated).

<Extended State>

[0106] When a tensile force (external force) is applied to the multilayer electrostatic actuator 1 in the layering direction Z, the non-connection region 15 (hinge portion 15) of the second film 3a.sub.2 of the actuator part 2a is elastically deformed (bent and extended), and the interval between the first film 3a.sub.1 and the second film 3a.sub.2 is widened (FIG. 4), resulting in the multilayer electrostatic actuator 1 extending in the layering direction Z (FIG. 1). FIG. 6 is a cross-sectional view illustrating the actuator part 2a in the extended state of the multilayer electrostatic actuator 1. As illustrated in FIG. 6, when a tensile force (external force) is applied in the layering direction Z. the interval between the first film 3a.sub.1 and the second film 3a.sub.2 is widened. Given that the spring displacement of the hinge portion 15 in this case is σ, the distance u from the conductive layer 21 of the first film 3a.sub.1 to the conductive layer 21 of the first film 3b.sub.1 (FIG. 3) is u.sub.extension = 2 × t.sub.23 + t.sub.23′ + σ.

[0107] As described above, the second connection regions 7b.sub.2 of the actuator part 2b act as ribs that prevent the first film 3a.sub.1 of the actuator part 2a from being deformed in the layering direction Z, and the deformation of the first film 3a.sub.1 is suppressed, so that deformation occurs in which the fixed end of the hinge portion 15 moves in the layering direction Z. The above discussion mainly about the actuator part 2a, 2b similarly applies to every actuator part 2a, 2b, 2c..... 2n, and thus the stroke U of the multilayer electrostatic actuator 1 including these n actuator parts 2 layered is U = n × (u.sub.extension - u.sub.initial) = n × σ.

4) Relationship Between Generated Force of Actuator Part and Resultant Force Of Electrostatic Force and Spring Force

[0108] FIG. 7 is a graph illustrating the relationship between the resultant force of the electrostatic force and the spring force of the multilayer electrostatic actuator 1 and the generated force F of the actuator part 2. The horizontal axis represents the spring displacement σ, and the vertical axis represents the generated force F of the actuator part 2. The spring force nonlinearly increases as the spring displacement σ increases, whereas the electrostatic force decreases approximately in inverse proportion to the square of σ as the spring displacement σ increases. In addition, the resultant force of the electrostatic force and the spring force draws a U-shaped curve as illustrated in the drawing. Given that the minimum value of the resultant force is Fmin, the generated force F of the actuator part 2 acts in the contraction direction with a magnitude of not less than Fmin.

Second Embodiment

[0109] In the multilayer electrostatic actuator 1 according to the first embodiment, the first film 3a.sub.1, 3b.sub.1 constituting the actuator part 2 is configured by the conductive film p. and the second film 3a.sub.2, 3b.sub.2 is configured by the insulating film Q. A multilayer electrostatic actuator 101 according to the second embodiment is different from the multilayer electrostatic actuator 1 according to the first embodiment in that both the first and second films constituting the actuator part are configured by the conductive film p.

1) Basic Structure of Multilayer Electrostatic Actuator

[0110] The basic structure of the multilayer electrostatic actuator 101 and the basic structure of the actuator part according to the second embodiment are the same as those of the multilayer electrostatic actuator 1 according to the first embodiment, and FIGS. 1 and 2 are applied in their entirety. In addition, elements identical or similar to those of the multilayer electrostatic actuator 1 according to the first embodiment are denoted by identical or similar reference signs, and the description thereof will be omitted.

2) Components of Multilayer Electrostatic Actuator

<Film>

[0111] As described above, in the multilayer electrostatic actuator 101 according to the second embodiment, both the first and second films 3a.sub.1, 3a.sub.2 constituting the actuator part are configured by the conductive film p illustrated in FIG. 3a.

<Connection Portion>

[0112] The connection portion of the actuator part of the multilayer electrostatic actuator 101 according to the second embodiment is the same as that of the multilayer electrostatic actuator 1 according to the first embodiment.

<Hinge Portion>

[0113] In the multilayer electrostatic actuator 1 according to the first embodiment, a voltage is applied between the first films 3a.sub.1, 3b.sub.1 of the overlapping actuator parts 2. The multilayer electrostatic actuator 101 according to the second embodiment is different from the multilayer electrostatic actuator 1 according to the first embodiment in that a voltage is applied between the overlapping first and second films 3a.sub.1, 3a.sub.2; 3b.sub.2, 3a.sub.1. When a voltage is applied between the first and second films 3a.sub.1, 3a.sub.2, the interval between the first and second films 3a.sub.1, 3a.sub.2 returns to the initial state due to the electrostatic attractive force (described later), resulting in the multilayer electrostatic actuator 101 contracting in the layering direction Z. The electrostatic attractive force caused by the voltage applied between the first film 3a.sub.1 and the second film 3a.sub.2 of the actuator part 2a acts to narrow the interval between the first and second films 3a.sub.1, 3a.sub.2. The gap between the other first and second films 3b.sub.1, 3b.sub.2 and the gap between the first film and the second film (e.g. 3b.sub.2 and 3a.sub.1) of different actuator parts 2 overlapping each other are similarly narrowed due to the electrostatic attractive force, resulting in the multilayer electrostatic actuator 101 contracting in the layering direction Z.

[0114] The basic structure of the actuator part of the multilayer electrostatic actuator 101 according to the second embodiment is the same as that of the actuator part 2 of the multilayer electrostatic actuator 1 according to the first embodiment: therefore, the second connection regions 7b.sub.2 of the actuator part 2b act as ribs with respect to the deformation of the non-connection region 15 of the first film 3a.sub.1 of the actuator part 2a in the layering direction Z. Therefore, when a tensile force (external force) is applied to the multilayer electrostatic actuator 101 in the layering direction Z. the non-connection region 15 of each of the second film 3a.sub.2 of the actuator part 2a and the second film 3b.sub.2 of the actuator part 2b is elastically deformed (bent and extended), but the deformation of the first film 3a.sub.1 of the actuator part 2a is suppressed. Thus, in the multilayer electrostatic actuator 101 according to the second embodiment, each actuator part has nonlinear spring characteristics as in the case of the multilayer electrostatic actuator 1 according to the first embodiment.

<Space>

[0115] The basic structure of the actuator part of the multilayer electrostatic actuator 101 according to the second embodiment is the same as that of the actuator part 2 of the multilayer electrostatic actuator 1 according to the first embodiment. Therefore, when a tensile force (external force) in the layering direction Z is applied to the multilayer electrostatic actuator 101, the second film 3a.sub.2 is elastically deformed, and the interval between the first and second films 3a.sub.1, 3a.sub.2 is separated, resulting in an increase in the opening area of the space 11, 13; whereas when a voltage is applied between the first and second films 3a.sub.1, 3a.sub.2 to cause an electrostatic attractive force, the interval between the first and second films 3a.sub.1, 3a.sub.2 is narrowed, resulting in a decrease in the opening area of the space 11, 13.

3) Manner of Operation of Multilayer Electrostatic Actuator

[0116] In the multilayer electrostatic actuator 101 having the above configuration, the extension/contraction state varies depending on whether a tensile force (external force) is applied in the layering direction Z and whether a voltage is applied between the first and second films 3a.sub.1, 3a.sub.2.

<Initial State (Contracted State)>

[0117] In the initial state or when a voltage is applied between the first and second films 3a.sub.1, 3a.sub.2 after application of a tensile force (external force) in the layering direction Z and an electrostatic attractive force acts and balances, the hinge portion 15 is not deformed, and the first film 3a.sub.1 and the second film 3a.sub.2 are in a planar state. At this time, the distance u from the conductive layer 21 of the first film 3a.sub.1 to the conductive layer 21 of the second film 3a.sub.2 (FIG. 3) is u.sub.initial = 2 × t.sub.23 (not illustrated).

<Extended State>

[0118] When a tensile force (external force) is applied to the multilayer electrostatic actuator 101 in the layering direction Z, the interval between the first film 3a.sub.1 and the second film 3a.sub.2 is widened. The distance u from the conductive layer 21 of the first film 3a.sub.1 to the conductive layer 21 of the second film 3a.sub.2 (FIG. 3) is u.sub.extension = 2 × t.sub.23 + σ. The above discussion mainly about the actuator part 2a. 2b similarly applies to every actuator part 2a. 2b, 2c,..., 2n, and thus the stroke U of the multilayer electrostatic actuator 101 including these n actuator parts layered is U = n × (u.sub.extension - u.sub.initial) = n × σ.

[0119] (2-4) Relationship between generated force of actuator part and resultant force of electrostatic force and spring force

[0120] Because the basic structure of the multilayer electrostatic actuator 101 according to the second embodiment is the same as that of the multilayer electrostatic actuator 1 according to the first embodiment, the relationship between the resultant force of the electrostatic force and the spring force of the actuator part and the generated force F of the actuator part in the multilayer electrostatic actuator 101 according to the second embodiment is also the same as that of the multilayer electrostatic actuator 1 according to the first embodiment, and FIG. 7 is applied in its entirety. However, in the second embodiment, the distance between the first film 3a.sub.1 and the second film 3a.sub.2 or between the second film 3b.sub.2 and the first film 3a.sub.1 is short as compared with the first embodiment in which contraction is caused by the electrostatic attractive force between the first films 3a.sub.1, 3b.sub.1 constituting the actuator part 2, and thus a large electrostatic attractive force is generated, which increases the contraction force.

5) Application Examples of Multilayer Electrostatic Actuator

[0121] For the manufacture of the multilayer electrostatic actuator 101 according to the second embodiment, a structure with high productivity is required. The following two application examples represent an example of a structure that allows for efficient manufacture with high productivity, in which the end portion of the actuator part 2 in each layer includes an outer hinge portion 17 connected to the end portion of the actuator part 2 of another layer. The outer hinge portion 17 eliminates the need for a post-process for connecting homopolar electrodes, leading to improvement in productivity. Furthermore, because the structures of these application examples do not have an electrode connection portion having a local discharge risk, the reliability of the multilayer electrostatic actuator is improved.

<Bent Structure>

[0122] FIG. 8 is a perspective view illustrating Application Example 1 in which the multilayer electrostatic actuator 1 illustrated in FIG. 1 is created with a bent structure. The multilayer electrostatic actuator 1A according to Application Example 1 has a paper spring structure in which two elongated ribbon-shaped electrodes 37, 39 are bent in a zigzag shape and alternately folded. The planar portions layered facing each other serve as the actuator parts 2 of different layers, and the loop-shaped connection portion extending outward from each actuator part 2 functions as the above-described outer hinge portion 17.

[0123] The multilayer electrostatic actuator part 1A with such a configuration can be efficiently manufactured as described above. In a multilayer electrostatic actuator without this configuration, the actuator parts are more likely to deform at positions closer to their end portions, which can make the distance between the actuator parts uneven. In contrast, in the multilayer electrostatic actuator part 1A, the outer hinge portion 17 functions as a semicylindrical structure that suppresses the deformation of the actuator part 2 in the plane direction; therefore, the end portion of the actuator part 2 has as uniform a distance as the central portion of the actuator part 2 between the connection surface portions 8 facing in the Z direction in each actuator part 2, which makes the movement in the layering direction Z stable and uniform, and can improve the driving force. Furthermore, the application of voltage to each actuator part 2 is performed simply on the two ribbon-shaped electrodes 37, 39 connected via the outer hinge portion 17, leading to simplified wiring.

<Wound Structure>

[0124] FIG. 9 is a perspective view illustrating Application Example 2 in which the multilayer electrostatic actuator 1 illustrated in FIG. 1 is created with a wound structure. The multilayer electrostatic actuator 1B according to Application Example 2 has a flat spiral wound structure in which the two elongated ribbon-shaped electrodes 37, 39 are wound in one direction from the center. The planar portions layered facing each other serve as the actuator parts 2 of different layers, and the loop-shaped connection portion extending outward from each actuator part 2 functions as the above-described outer hinge portion 17.

[0125] The multilayer electrostatic actuator 1B with such a configuration can also be efficiently manufactured, similarly to the multilayer electrostatic actuator 1A with the bent structure. In addition, the application of voltage to the actuator part 2 in each layer is performed simply on the two ribbon-shaped electrodes 37, 39 connected via the outer hinge portion 17, leading to simplified wiring.

Other Embodiments

[0126] The above-described embodiments are the basic embodiments of the present invention. The multilayer electrostatic actuator 1 according to the present embodiment is not limited to the above-described embodiments, and it is possible to change or remove a partial configuration without departing from the scope of the present embodiment, or to add a technique known and commonly used by those skilled in the art. For example, the planar shape of the multilayer electrostatic actuator 1 is not limited to the quadrangle described in the above-described embodiments, and may be another polygon such as a triangle or a pentagon, or may be a shape having a curve such as a circle, a semicircle, an oval, or an ellipse. In addition, the intersection angle θ of the actuator part 2 in each layer is not limited to 90° described in the above-described embodiments, and can be set to another angle such as 60° in the case that the planar shape of the multilayer electrostatic actuator 1 is a triangle, or 72° in the case that the planar shape is a pentagon.

[0127] FIGS. 7-1 is an explanatory diagram for explaining the overlapping state of two actuator parts of the multilayer electrostatic actuator according to another embodiment, where (a) is a view as viewed in the layering direction Z, and (b) is a cross-sectional view taken along VII-VII in (a). The multilayer electrostatic actuators 1 according to the first and second embodiments are both configured by layering the actuator parts 2a, 2b at the intersection angle θ of 90°, from which the multilayer electrostatic actuator according to another embodiment is different in that the actuator parts 2a, 2b are layered at the intersection angle θ of an acute angle different from 90°. Elements identical or similar to the elements of the embodiments described above are denoted by identical or similar reference signs, and the description thereof will be omitted. The first connection regions 7a.sub.1 (indicated by solid lines) and the second connection regions 7b.sub.2 (indicated by broken lines) of the second film 3b.sub.2 are arranged on the upper and lower sides of the first film 3a.sub.1 illustrated in (a), and the second connection regions 7a.sub.2 (indicated by solid lines) and the first connection regions 7a.sub.1 (indicated by broken lines) are arranged on the upper and lower sides of the second film 3a.sub.2 illustrated in (b).

[0128] As viewed in the layering direction Z, as illustrated in FIG. 7-1a, the axes of the pattern of the first connection regions 7a.sub.1 arranged on the first film 3a.sub.1 of the actuator part 2a and the axes of the pattern of the second connection regions 7b.sub.2 of the second film 3b.sub.2 of the actuator part 2b placed under the actuator part 2a intersect at the intersection angle θ of an acute angle different from 90°. Therefore, when a tensile force (external force) in the layering direction Z is applied to the multilayer electrostatic actuator, the deformation of the first film 3a.sub.1 is suppressed. On the other hand, as illustrated in FIG. 7-1b, the axes of the pattern of the second connection regions 7a.sub.2 arranged on the second film 3a.sub.2 and the axes of the pattern of the first connection regions 7a.sub.1 arranged on the first film 3a.sub.1 are parallel to each other and do not intersect each other. Therefore, when a tensile force (external force) in the layering direction is applied to the multilayer electrostatic actuator, the second film 3a.sub.2 is deformed.

[0129] FIGS. 7-2 is an explanatory diagram for explaining the condition of intersection between the first connection regions 7a.sub.1 and the second connection regions 7b.sub.2 in the multilayer electrostatic actuator illustrated in FIGS. 7-1. The patterns of the first connection regions 7a.sub.1 and the second connection regions 7b.sub.2 both form linear shapes having a substantially uniform width d and arranged at equal intervals. Given that the length, on the plane as viewed in the layering direction Z, of the axes of the pattern of one of the first connection regions 7a.sub.1 of the actuator part 2a and the second connection regions 7b.sub.2 of the actuator part 2b is L. and the width between the non-connection regions in the one connection regions as viewed in the layering direction Z is 2 × ℓ + d (see FIG. 6), the intersection angle θ [rad] of the axes of the patterns between the two connected actuator parts 2a, 2b as viewed in the layering direction Z satisfies

[00002]$\begin{array}{cc}\arctan \left(\frac{2\times l+d}{L}\right)<\left|\theta \right|\le \frac{\pi }{2}.& \text{­­­[Formula 2]}\end{array}$

[0130] In addition, the shape and arrangement (pattern) of the connection regions 7 is not limited to the shape and arrangement described in the above-described embodiments. It is possible to adopt various other shapes and arrangements (patterns) such as those in which the connection regions 7 with a circular shape or a quadrangular shape in plan view are arranged at equal intervals in the width direction X and the depth direction Y. Furthermore, in the above description, both the first connection regions and the second connection regions of the actuator part 2 in each layer are formed in linear shapes having a uniform width and arranged at equal intervals such that one first connection region is positioned at the center of the space between two second connection regions as viewed in the layering direction Z. However, as long as the first connection regions and the second connection regions do not overlap each other as viewed in the layering direction Z, the first connection regions and the second connection regions do not need to be linear or be arranged at equal intervals.

TABLE-US-00001 REFERENCE SIGNS LIST 1, 101, 1A, 1B multilayer electrostatic actuator 2, 2a, 2b, 2c actuator part 3 film 3a.sub.1, 3b.sub.1 first film 3a.sub.2, 3b.sub.2 second film 5a, 5b end member 7 connection region 7a.sub.1, 7b.sub.1 first connection region 7a.sub.2, 7b.sub.2 second connection region 8.sub.1, 8.sub.2 connection surface portion 11 space 13 space 15 non-connection region (or hinge portion) 17 outer hinge portion 21 conductive layer 23 insulating layer 37 ribbon-shaped electrode 39 ribbon-shaped electrode θ intersection angle Z layering direction X width direction Y depth direction X, Y planar direction U stroke u distance σ spring displacement d width (of connection region) ℓ length (of hinge portion) O supporting point F generated force (of actuator part) Z layering direction