WO2002037892A2

WO2002037892A2 - Operating element

Info

Publication number: WO2002037892A2
Application number: PCT/DK2001/000718
Authority: WO
Inventors: Peter Gravesen; Mohamed Yahia Benslimane
Original assignee: Danfoss A/S
Priority date: 2000-11-02
Filing date: 2001-10-31
Publication date: 2002-05-10
Also published as: AU2002212104A1; WO2002037892A3; DE10054246C2; DE10054246A1

Abstract

An operating element is disclosed, comprising a body made from an elastomeric material, with an electrode arrangement (3) provided on each of the two opposing limiting surfaces, of which at least one comprises several first electrodes (7) penetrating the limiting surface in a perpendicular direction (6) thereto. The aim of the invention s to improve the dynamics of such an operating element. Said aim is achieved, whereby the electrode arrangement (3) comprises second electrodes (9), several of which are located in spaces (8, 8a, 8b) between neighbouring first electrodes (7) connecting the same, whereby the second electrodes (9, 9') in neighbouring spaces (8a, 8b) are arranged offset from each other.

Description

actuator

The invention relates to an actuating element with a body made of an elastomer material, which is provided on two mutually opposite boundary surfaces, each with an electrode arrangement, at least one of which has a plurality of first electrodes passing through in the transverse direction of its boundary surface.

Such an actuator is known from US 5 977 685.

Such actuators are also called "artificial muscles" because their behavior corresponds to that of human muscles under certain conditions.

The way it works is relatively simple. When a voltage difference is applied to the two electrode assemblies, an electric field is created through the body, the electric field creating mechanical attractive forces between the electrode assemblies. This leads to an approximation of the two electrode arrangements and, associated therewith, to a compression of the body. The approximation can still be supported if the material of the body has dielectric properties. However, since the material has an essentially constant volume, the compression, that is to say the reduction in the thickness, leads to an increase the dimensions of the body in the other two directions, ie parallel to the electrode arrangements.

If one now limits the elasticity of the body to one direction, the change in thickness is completely converted into a change in length in the other direction. For the following explanation, the direction in which the length change is to take place is referred to as the "longitudinal direction". The direction in which a change in length should not take place is referred to as the "transverse direction". In the known case, the electrode arrangement has a conductive layer with a relatively low conductivity, to which strips made of a non-compliant material are applied in the transverse direction, the strips being spaced apart from one another in the longitudinal direction. The conductive layer is intended to ensure that the electrical field is distributed as uniformly as possible, while the strips, preferably made of a metal, are intended to prevent the body from spreading in the transverse direction. However, due to the poor conductivity of the electrically conductive layer, there is a certain limitation in the dynamics.

The invention has for its object to improve the mechanical extensibility of an actuating element.

In the case of an actuating element of the type mentioned at the outset, this object is achieved in that the electrode arrangement has second electrodes, of which each because several are arranged in gaps between adjacent first electrodes and connect these, the second electrodes being arranged offset in relation to one another in adjacent gaps.

With this configuration, two advantages are combined. The first electrodes which pass in the transverse direction limit the elasticity of the body in this transverse direction or even exclude it. "Passing through" is intended to express that the first electrodes have a shape that can no longer be stretched, for example a straight line. So you ensure that a compression of the body can be converted almost completely into a change in length. In practice, of course, there will also be minor changes in the transverse direction. However, compared to the changes in the longitudinal direction, these are negligible. The second electrodes now ensure that a relatively high electrical conductivity is obtained over the entire surface of the boundary surface. This improves the mechanical extensibility of the actuating element, and the actuating element can be operated at high frequencies. Because of the special arrangement of the second electrodes between the first electrodes, the second electrodes do not significantly increase the rigidity in the longitudinal direction. Rather, the first and the second electrodes form meshes between them, which can pull apart in a diamond shape when the length changes. An additional effect is even achieved: the

Changing the length leads to an additional tension in the transverse direction, which counteracts expansion of the body in the transverse direction, since the effective length of the first electrodes in the transverse direction is reduced. A significantly improved conversion of the approach movement of the electrodes into a change in length is thus obtained. The mechanical extensibility is improved without the dynamics of the actuating element being significantly impaired.

Preferably, the second electrodes of every nth gap lie on a line in the longitudinal direction. This simplifies the design of the electrode arrangement. At the same time, the electrical field distribution can be better controlled.

Preferably, the second electrodes of each second gap lie in a line in the longitudinal direction. A structure of the electrode arrangement in the manner of a grid or network with nodes arranged offset from one another is thus achieved. Such a grid can be in

Pull apart relatively easily in the longitudinal direction, while it is relatively rigid in the transverse direction.

The second electrodes of a gap are preferably arranged in the middle of a distance between two adjacent electrodes of an adjacent gap. This results in a high symmetry when the second electrodes are loaded and a very uniform structure of the electric field. The electrode arrangement is preferably connected directly to the body. This configuration has several advantages. On the one hand, the production of such an actuating element is simplified because there is no need to apply an intermediate layer between the electrode arrangement and the body. On the other hand, it is also possible to connect the electrode arrangement to the body more firmly, ie more permanently and more reliably. The attachment can only be matched to the material pairing between the electrode arrangement and the body.

The distance between two first electrodes is preferably not greater than the thickness of the body between the boundary surfaces. With this configuration, an electric field is generated between the two electrode arrangements which is so uniform that uniform compression of the body can be achieved.

The extension of a first electrode in the longitudinal direction preferably corresponds to the distance between two first electrodes. In other words, the length of the second electrodes in the longitudinal direction is exactly the same as the length of the first electrodes in the longitudinal direction. This further contributes to an equalization of the electrical field. Since a relatively large area is available for conducting electrical current, the response time of such an actuating element is only slightly impaired in comparison to a full-area electrode. A lateral offset between two adjacent second electrodes is preferably greater than the distance between two first electrodes. In this way, a particularly good stretchable mesh or grid is achieved.

The electrode arrangement is preferably composed of a multiplicity of congruent unit cells. These unit cells all have the same shape. However, they can be built up mirror-inverted to each other. The body is usually formed by a relatively thin film. This film ensures that the distance between the opposing electrode arrangements is not too great and that an electric field building up between the electrode arrangements can exert sufficient force to compress the body. The thinner the body, the finer the structure of the electrode arrangements. A preferred manufacturing process for the electrode arrangements is photolithography. In photolithography, production becomes easier if you can repeat a basic pattern, in this case the unit cell, many times.

Adjacent unit cells are preferably mirrored to one another. The network or lattice-like structure described above is thereby achieved in a simple manner.

Each unit cell preferably has a strip which runs in the transverse direction and which is located on both ends. each has a projection which is directed in the longitudinal direction, the two projections being directed in opposite directions. Depending on the point of view, the unit cell has the shape of an elongated S or Z. If several such unit cells are assembled in the transverse direction, the strips form the first electrode.

The unit cell preferably has a width / height ratio which is greater than or equal to 3%. In this embodiment, the unit cell has a sufficient transverse extent to allow the desired change in length when it is assembled with other unit cells to form the electrode arrangement.

The invention is described below with reference to a preferred embodiment in connection with the drawing. Show here:

1 is an actuating element in a schematic side view in two states,

2 shows a schematic top view of the actuating element and

Fig. 3 shows a unit cell.

1 shows an actuating element 1 in two states, namely in FIG. 1 a in the idle state and in FIG. 1 b in the actuated state. The actuating element 1 has a body 2 made of an elastomer film, for example a silicone elastomer. Such a film usually also has dielectric properties. Above all, the body 2 has the property that its volume remains constant when it is compressed. Accordingly, the reduction in the thickness d of the body 2 causes an expansion perpendicular to the printing direction, as can be seen from a comparison between FIGS. 1a and 1b.

The body 2 has an electrode arrangement 3 on its upper side and a further electrode arrangement 4 on its underside. The two electrode arrangements 3, 4 have the same or at least a similar design. If a voltage difference is applied to the two electrode arrangements 3, 4, an electrical field is created which penetrates the body 2. This electric field generates forces which cause the two electrode arrangements 3, 4 to be attracted. The attractive forces of the two electrode arrangements 3, 4 press the body 2 together.

As mentioned above, the body 2 has a constant volume, ie a reduction in the thickness d (from FIG. 1 a to FIG. 1 b) results in a corresponding expansion in width and length. If you now prevent the expansion in width, the reduction in thickness only affects an increase in length. For the purposes of the following explanation, it is assumed that the longitudinal direction, which is represented by an arrow 5 in FIGS. 1 and 2, runs from left to right in FIG. 1 and from bottom to top in FIG. 2, while the transverse direction , which is represented by an arrow 6, runs from left to right in FIG. The actuating element 1 is therefore anisotropic. Changes in the longitudinal direction 5 are possible, while changes in the transverse direction 6 are practically prevented.

In order to constructively effect this anisotropy, the electrode arrangements 3, 4 have a specific design, which is explained below in connection with FIGS. 2 and 3.

The electrode arrangement 3 is shown in plan view in FIG. 2. The electrode arrangement 4 looks exactly the same.

The electrode arrangement 3 has first electrodes 7 which extend in the transverse direction 6 in the form of a line over the entire width of the body 2. The first electrodes 7 are arranged with gaps 8, 8a, 8b to one another. In these gaps 8, second electrodes 9 are arranged in such a way that an electrode 9 'of a gap 8a is arranged in the middle between two second electrodes 9 of the adjacent gap 8b. The second electrodes 9 'of every second gap 8 lie here on a straight line in the longitudinal direction 5. The first and second electrodes are perpendicular to the direction of expansion. device attached to the actuator. The electrode arrangement 3 thus forms a network or grid with meshes 10, each of which is bounded by two first electrodes 7 and two second electrodes 9, these meshes 10 being contracted in a diamond shape when the body 2 expands in the longitudinal direction 5.

The electrode arrangements 3, 4 are applied directly to the body 2, i.e. without an electrically poorly conductive intermediate layer. They can thus be connected relatively firmly to the body 2, so that the movement of the body 2, i.e. A change in the extension in the longitudinal direction 5 or transverse direction 6 is only permissible as far as the electrode arrangements 3, 4 allow.

Accordingly, a change in the extent of the body 2 in the transverse direction 6 is prevented by the first electrodes 7. Basically, these are not stretchable, so that the body 2 must not expand in the transverse direction 6. It looks different in the longitudinal direction 5. When the body 2 expands in the longitudinal direction 5, the meshes 10, which are slit-shaped in the rest state, are deformed like a diamond. This creates an additional pull in the transverse direction 6, which counteracts an expansion of the body 2 in the transverse direction 6.

In order to ensure a uniform formation of the electrical field between the two electrode arrangements 3, 4, it is provided that the distance a between two first electrodes is not greater than the thickness d of the body 2 between the boundary surfaces, ie between the electrode arrangements 3, 4. It can also be seen from FIG. 2 that the first electrodes 7 have a longitudinal extension b which corresponds to the distance a, ie the longitudinal extension of the gaps 8.

The electrode arrangement 3 consists of a regular pattern of so-called unit cells 11, one of which is shown enlarged in FIG. 3. In Fig. 2, four such unit cells 11 are drawn in with dashed lines, whereby it can be seen that adjacent unit cells 11 are each mirrored to one another, i.e. they are either mirrored on a line 12 which runs parallel to the longitudinal direction 5, or on a line 13 which runs parallel to the transverse direction 6.

Each unit cell 11 has a strip 14 which has the above-mentioned width b and a length L and later forms the first electrodes 7, and two projections 15, 16, so that the unit cell 11 has an extension H overall. While the strip 14 is directed in the transverse direction 6, the projections 15, 16 are directed in the longitudinal direction 5, but are opposed to one another. The ratio L / H is at least 3 ^1/2 • It may also be even larger, for example 10. Usually, the extension H twice the length b of the first electrode, so that during assembly of the respective unit cells 11 shown in Fig. 2 illustrated patterns of electrical the arrangement wins, in which the gaps 8 between the first electrodes 7 are as large as the longitudinal extent b of the first electrodes 7.

The second electrode 9 'is offset from an adjacent electrode 9 by a distance L extending in the transverse direction. This offset should be greater than the distance a between two first electrodes 7, i.e. L> a.

As mentioned above, it is advantageous if the distance a between the first electrodes 7 is equal to or less than the thickness d of the body 2. If one works with thin films with a thickness in the micrometer range, photolithography techniques are well suited to design the electrode arrangements 3, 4. For example, a thin layer of gold can be applied to the body 2, for example by vapor deposition. A thin, for example 1 μm thick, positive photoresist layer is then applied to the gold-coated body 2. The photoresist is exposed to UN radiation, if necessary after curing, through a mask which is designed in such a way that it has exactly the desired profile pattern for the electrode arrangement 3, 4. The photoresist is then developed and the exposed parts are removed. The body is then placed in a (KI + I ₂ ) mixture that etches out unwanted gold surfaces, namely the meshes 10 or slots that are to be formed in the gold coating. The pattern shown in FIG. 2 is thus achieved. (KI is iodine potassium and I ₂ is iodine.) Due to the special shape of the electrode arrangements 3, 4, the electrostatic field is distributed uniformly over the body 2, as a result of which an optimal degree of efficiency is achieved. Here, the second electrodes 9 act as bridges between the first electrodes 7. The meshes 10, however, do not conduct. For this reason, the electrode arrangement 3, 4 has an increased resistance compared to a continuous gold coating of the same thickness. You can roughly estimate this increased resistance with a resistance increase factor K _R

K _R = (L / H) ² (l / α + H / L),

the dimensions H and L emerge from FIG. 3 and = b / H (fill factor).

A similar force factor K can be calculated from the same values using the following formula:

K _F = α ³ (H ² / ((L-αH) L))

A comparison of the two factors K _R and K _{F leads to} the conclusion that it is possible to form an actuating element with reduced force (increased extensibility) without increasing the electrical resistance.

Theoretically, it can be assumed that if L / H = 10 and the thickness d of the body is increased by a factor of 100, the net result is unchanged electrical resistance and a force reduced by a factor of 100 or an extensibility increased by a factor of 100.

However, this is only valid for a freely suspended body 2. When the body is bonded to a substrate, the net reduction is much smaller if the characteristic dimensions of the slots or meshes 10 are greater than the thickness d of the layer to which the electrode assembly is attached. In other words, when working with thin layers in the range from 1 to 2 μm, submicro-photolithography is required to expose the meshes 10. Cost-effective processes, such as masking or printing techniques, limit the minimum mesh width in the longitudinal direction to 20 to 50 μm and thus the minimum elastomer thickness to 50 to 100 μm.

The table below shows typical values for electrode layers and elastomers as well as typical values for the activation voltage of an actuator.

In the following we consider a 20 μm thick silicone elastomer film with an elastic modulus of 0.7 MPa and a dielectric constant of 3. The electrical they are made of gold and have a thickness of 0.05 μm and a modulus of elasticity of 80,000 MPa. The capacitance of such an actuator is 0.1 nF / cm ² , and the step response is of the order of microseconds for the unloaded actuator. Assuming an electrode stretch factor of 4000, 1000 V is required to produce an extension of the order of 10%, whereas an extension of less than 0.05% is produced in the case of an invisible electrode, ie an electrode with one Elongation factor of 1. In other words, the invention makes it possible to lower the activation voltage.

Claims

claims

1. Actuating element with a body made of an elastomer material, which is provided on opposing boundary surfaces, each with an electrode arrangement, at least one of which has a plurality of first electrodes passing through in the transverse direction of its boundary surface, characterized in that the electrode arrangement (3, 4) has second electrodes ( 9, 9 '), of which several are arranged in gaps (8, 8a, 8b) between adjacent first electrodes (7) and connect them, the second electrodes (9, 9') being arranged in adjacent gaps (8a, 8b ) are staggered.

2. Actuating element according to claim 1, characterized in that the second electrodes (9, 9 ') of every nth gaps (8, 8a, 8b) lie on a line in the longitudinal direction (5).

3. Actuating element according to claim 2, characterized in that the second electrodes (9, 9 ') of every second gap (8a, 8b) lie in a line in the longitudinal direction (5).

4. Actuating element according to one of claims 1 to 3, characterized in that the second electrodes (9, 9 ') of a gap (8a) in the middle of a distance between two adjacent second electrical (9) an adjacent gap (8b) are arranged.

5. Actuator according to one of claims 1 to 4, characterized in that the electrode arrangement (3, 4) is connected directly to the body (2).

6. Actuating element according to one of claims 1 to 5, characterized in that the distance (a) between two first electrodes (7) is not greater than the thickness (d) of the body (2) between the boundary surfaces.

7. Actuator according to one of claims 1 to

6, characterized in that the extent (b) of a first electrode (7) in the longitudinal direction corresponds to the distance (a) between two first electrodes (7).

8. Actuator according to one of claims 1 to

7, characterized in that a lateral offset between two adjacent second electrodes is greater than the distance between two first electrodes.

9. Actuator according to one of claims 1 to

8, characterized in that the electrode arrangement (3, 4) is composed of a plurality of congruent unit cells (11).

10. Actuating element according to claim 9, characterized in that adjacent unit cells (11) are formed mirrored to one another.

11. Actuating element according to claim 9 or 10, characterized in that each unit cell (11) has a strip (14) which extends in the transverse direction (6) and which has a projection (15, 16) at both ends, which in the longitudinal direction (5) is directed, the two projections (15, 16) being directed in opposite directions.

12. Actuating element according to one of claims 9 to 11, characterized in that the unit cell has a width / height ratio (L / H) which is greater than or equal to 3 ¹ / -. is.