WO2014110798A1

WO2014110798A1 - Electrostatic actuator and manufacturing method thereof

Info

Publication number: WO2014110798A1
Application number: PCT/CN2013/070701
Authority: WO
Inventors: Sheng Lai; Ming Li
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-01-18
Filing date: 2013-01-18
Publication date: 2014-07-24
Also published as: CN104737436A; CN104737436B; DE112013006449B4; DE112013006449T5

Abstract

The present invention relates to electrostatic actuator and manufacturing method thereof, wherein the electrostatic actuator comprising: an elastic ribbon; and a plurality of electrode plate pairs, each electrode plate pair of which sandwiches the elastic ribbon, wherein the plurality of electrode plate pairs is piled up into a multi-layer structure through folding of the elastic ribbon. Compared to the prior art, the electrostatic actuator can be manufactured easily.

Description

Electrostatic Actuator and Manufacturing Method Thereof Technical Field

The present invention relates to an actuator, and particularly to an electrostatic actuator and manufacturing method thereof.

Background Art

An electrostatic actuator is a device whose moving elements are driven by the electrostatic force according to Coulomb's law. The typical structure of an electrostatic actuator is composed of two parallel electrode plates A, as show in Fig. 1. When a voltage potential is applied between the two parallel electrode plates, the moving electrode plate will move towards to the fixed electrode plate. After the voltage potential applied to the two parallel electrode plates is removed, the moving electrode plate returns to its original position by a restoring spring force, for example, from supporting flexures. Electrostatic actuators are widely applied in many applications due to their low power consumption and fast response, such as accelerometer, deformable optics, relays and valves.

The attractive force F generated in the electrostatic actuator shown in Fig. 1 can be calculated according to the following formula (1):

Where V is the applied voltage, d is the gap distance between the two parallel electrode plates, ε is the permittivity of the medium between the electrode plates, and A is the area of the electrode plates. According to the above formula (1), the attractive force is an inverse square function of the gap distance. Therefore, the initial gap distance between the moving electrode plate and the fixed electrode plate can not be large, or else the attractive force will be very small. On the other hand, during the moving process, the attractive force will increase more rapidly than the spring force as the gap distance decreases. It is well established that, when the gap distance between the two electrode plates is less than 2/3 of the initial gap distance, or the travel distance of the moving electrode plate is larger than 1/3 of the initial gap distance, the restoring spring force from the supporting flexures cannot offset the electrostatic force and the pull-in instability occurs. In some cases, the pull-in instability can damage the electrostatic actuator since it can be impossible to separate the electrode plates afterwards. Therefore, the stable travel distance of a conventional electrostatic actuator is typically limited to 1/3 of the initial gap distance. Increasing the initial gap between the electrode plates is the simplest solution for increasing the stable travel distance, but this solution results in a low output force or a high driving voltage, which are undesirable in numerous applications.

Japanese researchers Y. Hata, K. Okuda and K. Saneyoshi proposed a stacked-type electrostatic actuator (See Y.Hata, K.Okuda and K. Saneyoshi, Development of Fish Robot Using Stacked-Type Electrostatic Actuators, the 17th International Conference on Electrical Machines, 2006). This stacked-type electrostatic actuator is constructed by alternately folding two ribbon electrodes around each other, wherein each of the two ribbon electrodes consists of a thin metallic conductor sandwiched between two thin plastic films. By applying electrical voltage to one of the two ribbon electrodes and grounding the other of the two ribbon electrodes, each electrode layer becomes charged and an attractive electrostatic force is generated. This stacked-type electrostatic actuator does not lose any driving force because the electrostatic force works perpendicularly to the electrodes, and it can achieve large displacements because many electrode parts are piled up perpendicularly. Therefore, the stacked-type electrostatic actuator may output high electrostatic force and achieve large stable travel distance than other electrostatic actuators.

However, manufacturation of the stacked-type electrostatic actuator is very complex because the ribbon electrodes need to be folded alternately to form a multi-layer configuration. This folding process will be even harder when the electrostatic actuator is miniaturized for the purpose of getting large electrostatic force per unit area, for example, each ribbon electrode is only several mm wide and 0.1mm thick.

Summary

Enbodiments of the present invention provide an electrostatic actuator and manufacturing method thereof, by which the electrostatic actuator can be manufactured easily.

An electrostatic actuator according to embodiments of the present invention may comprise: an elastic ribbon; and a plurality of electrode plate pairs, each electrode plate pair of which sandwiches the elastic ribbon, wherein the plurality of electrode plate pairs is piled up into a multi-layer structure through folding of the elastic ribbon.

In an implementation, a gap distance between any two adjacent electrode plate pairs of the plurality of electrode plate pairs is identical.

In an implementation, the elastic ribbon is insulated.

In an implementation, electrode plates of the plurality of electrode plate pairs have the same shape and dimension.

In an implementation, the plurality of electrode plate pairs is parallel to each other.

In an implementation, the elastic ribbon includes active polymer parts and passive polymer parts connected alternately, wherein the elastic ribbon is folded at the active polymer parts and each electrode plate pair of the plurality of electrode plate pairs sandwiches the elastic ribbon on one of the passive polymer parts.

In an implementation, the active polymer parts are polyimide hinges that shrink at a prefined temperature or shape-memory polymer elements that actuate with resistive heating.

In an implementation, a surface of each of electrode plates of the plurality of electrode plate pairs is coated with insulated material.

A method for manufacturing an electrostatic actuator according to embodiments of the present invention may comprise: installing a plurality of electrode plate pairs on an elastic ribbon at a predefined interval, wherein each electrode plate pair of the plurality of electrode plate pairs sandwiches the elastic ribbon; and folding the elastic ribbon to pile up the plurality of electrode plate pairs into a multi-layer configuration.

In an implementation, the elastic ribbon includes active polymer parts and passive polymer parts connected alternately, the step of installing further includes installing each electrode plate pair of the plurality of electrode plate pairs on one of the passive polymer parts, and the step of folding further includes coating black ink on one surface of each of the active polymer parts so that surfaces with the black ink of any two adjacent active polymer parts of the active polymer parts are opposite surfaces, and heating the active polymer parts to fold the elastic ribbon at the active polymer parts.

In an implementation, a gap distance between any two adjacent electrode plate pairs of the plurality of electrode plate pairs in the multi-layer configuration is identical.

In an implementation, the elastic ribbon is insulated.

In an implementation, the plurality of electrode plate pairs in the multi-layer configuration is parallel to each other.

As stated above, embodiments of the present invention manufacture the electrostatic actuator through folding of single elastic ribbon, so compared with the prior art, the electrostatic actuator can be manufactured easily. Description of Drawings

These and other features and advantages of the present invention will become apparent through the following detailed description in conjunction with accompanying drawings.

Fig.1 shows a diagram of an existed electrostatic actuator.

Fig- 2 shows a diagram of an electrostatic actuator according to an embodiment of the present.

Fig.3 shows a flowchart of a method for manufacturing an electrostatic actuator according to an embodiment of the present. Fig.4 shows a diagram of coating black ink on active polymer parts according to an embodiment of the present.

Mode for Carrying Out the Invention

Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embidiments can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embidments. Fig.2 shows a diagram of an electrostatic actuator according to an embodiment of the present. As shown in Fig.2, an electrostatic actuator 20 may include an insulated elastic ribbon 200 and four electrode plate pairs 210-240.

The insulated elastic ribbon 200 may include three active polymer parts 204 and four passive polymer parts 208 connected alternately. The three active polymer parts 204 may be polyimide hinges that shrink at a predefined temperature or shape memory polymer elements that actuate with resistive heating, and thus the insulated elastic ribbon 200 can fold at the three active polymer parts 204 when the three active polymer parts 204 are heated.

The electrode plate pair 210 may include two electrode plates 212 and 214, the electrode plate pair 220 may include two electrode plates 222 and 224, the electrode plate pair 230 may include two electrode plates 232 and 234, and the electrode plate pair 240 may include two electrode plates 242 and 244. The electrode plates 212, 214, 222, 224, 232, 234, 242 and 244 may be of square and have the same dimension L*L. Each electrode plate pair of the four electrode plate pairs 210-240 sandwiches the insulated elastic ribbon 200 on one of the four passive polymer parts 208.

The four electrode plate pairs 210-240 are piled up into a multi-layer configuration through folding of the insulated elastic ribbon 200 at the three active polymer parts 204. In the multi-layer configuration, the four electrode plate pairs 210-240 may be parallel to each other.

In the multi-layer configuration, there are the same gap distances d between any two adjacent electrode plate pairs, i.e., between the electrode plate pair 210 and the electrode plate pair 220, between the electrode plate pair 220 and the electrode plate pair 230, and between the electrode plate pair 230 and the electrode plate pair 240. In other words, the gap distances d between any two adjacent electrode plate pairs of the four electrode plate pairs 210-240 are identical in the multi-layer configuration. In order to enable the electrostatic actuator 20 to output high electrostatic force, the electrostatic actuator 20 may be designed so that the gap distances d between adjacent electrode plate pairs of the four electrode plate pairs 210-240 are small when the electrostatic actuator 20 relaxes and is in its original state.

In order to enable the electrostatic actuator 20, a charging process is initiated to apply opposite charges to opposite electrode plates of adjacent electrode plate pairs of the four electrode plate pairs 210-240. During the charging process, the opposite voltages are applied to the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240, i.e., opposite electrode plates 214 and 222 of the adjacent electrode plate pairs 210 and 220, opposite electrode plates 224 and 232 of the adjacent electrode plate pairs 220 and 230, and opposite electrode plates 234 and 242 of the adjacent electrode plate pairs 230 and 240, and positive and negative charges begin to accumulate on the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240 respectively. Attractive electrostatic force will be generated between the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240 due to the positive and negative charges accumulated on the opposite electrode plates and become larger and larger as more and more charges are accumulated on the opposite electrode plates. The gap distances between adjacent electrode plate pairs of the four electrode plate pairs 210-240 are reduced due to the generated attractive electrostatic force and thus the electrostatic actuator 20 shrinks.

When the electrostatic actuator 20 shrinks up to a predefined level, the charging process is finished and the opposite voltages are removed. In this case, the attractive electrostatic force will still be generated between the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240 because of the positive and negative charges accumulated on the opposite electrode plates and thus the electrostatic actuator 20 keeps shrinking.

When the positive and negative charges accumulated on the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240 are removed to disable the electrostatic actuator 20, no attractive electrostatic force is generated between the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240, the gap distances between adjacent electrode plate pairs of the four electrode plate pairs 210-240 are extended due to elastic force of the elastic ribbon 200, and the electrostatic actuator 20 relaxes and resume to its original state.

Fig.3 shows a flowchart of method for manufacturing the electrostatic actuator according to an embodiment of the invention. As shown in Fig.3, at Step S310, the four electrode plate pairs 210-240 are installed on the insulated elastic ribbon 200 in a manner that each electrode plate pair of the four electrode plate pairs 210-240 sandwiches the insulated elastic ribbon 200 on one of the four passive polymer parts 208 of the insulated elastic ribbon 200.

At Step S320, black ink is coated on one surface of each of the three active polymer parts 204 of the insulated elastic ribbon 200 so that surfaces with black ink of any two adjacent active polymer parts of the three active polymer parts 204 are opposite surfaces, as shown in Fig.4.

At Step S330, the three active polymer parts 204 of the insulated elastic ribbon 200 are heated for example by placing the insulated elastic ribbon 200 under an infrared light. The surfaces with black ink of the three active polymer parts 204 will heat up faster than the surfaces with no black ink of the three active polymer parts 204 due to the effective light absorption by the black ink, so the insulated elastic ribbon 200 is folded at the three active polymer parts 204 to pile up the four electrode plate pairs 210-240 into the multi-layer configuration. Clearly from the above description, the electrostatic actuator 20 can be manufactured only through folding of single insulated elastic ribbon 200, so the electrostatic actuator 20 can be manufactured easily. Moreover, the electrostatic actuator 20 consumes power only during the charging process, but the charging process is very fast, for example, it lasts for roughly 200 microseconds, and therefore the electrostatic actuator 20 may only consume little power when it works.

Other Embodiments

Those skilled in the art will understand that in the above embodiment, the gap distances between any two adjacent electrode plate pairs of the four electrode plate pairs 210-240 in the multi-layer configuration are identical, but the present invention is not so limited. In some other embodiments of the present invention, the gap distances between adjacent electrode plate pairs of the four electrode plate pairs 210-240 may be different.

Those skilled in the art will understand that in the above embodiments, the electrode plates 212, 214, 222, 224, 232, 234, 242 and 244 are of square, but the present invention is not so limited. In some other embodiments of the present invention, the electrode plates 212, 214, 222, 224, 232, 234, 242 and 244 are of other shape.

Those skilled in the art will understand that in the above embodiments, the three active polymer parts 204 of the insulated elastic ribbon 200 are heated by placing the insulated elastic ribbon 200 under an infrared light, but the present invention is not so limited. In some other embodiments of the present invention, the three active polymer parts 204 of the insulated elastic ribbon 200 may be heated by only placing the three active polymer parts 204 of the insulated elastic ribbon 200 under the infrared light.

Those skilled in the art will understand that in the above embodiments, the insulated elastic ribbon 200 include three active polymer parts 204 and four passive polymer parts 208 connected alternately, but the present invention is not so limited. In some other embodiments of the present invention, the insulated elastic ribbon 200 may be made totally from the active parts, the four electrode plate pairs 210-240 are installed on the insulated elastic ribbon 200 at a predefined interval and only these parts of the insulated elastic ribbon 200 between any two adjacent electrode plate pairs of the four electrode plate pairs 210-240 are heated to fold the insulated elastic ribbon 200 when the electrostatic actuator 20 is manufactured.

Those skilled in the art will understand that in the above embodiments, the insulated elastic ribbon 200 is made from the polymer parts which can be heated to fold the insulated elastic ribbon 200, but the present invention is not so limited. In some other embodiments of the present invention, the insulated elastic ribbon 200 is made from an element which can be manipulated by a machine to fold the insulated elastic ribbon 200.

Those skilled in the art will understand that two copper wires may be embedded within the insulated elastic ribbon 200 to apply voltages to the electrode plates 212, 214, 222, 224, 232, 234, 242 and 244, wherein one of the two copper wires is connected to the electrode plates 212, 222, 232 and 242, the other is connected to the electrode plates 214, 224, 234 and 244.

Those skilled in the art will understand that in the above embodiments, the electrode plates 212, 214, 222, 224, 232, 234, 242 and 244 have the same dimension, but the present invention is not so limited. In some other embodiments of the present invention, the electrode plates 212, 214, 222, 224, 232, 234, 242 and 244 may have different dimension.

Those skilled in the art will understand that insulated material may be coated on a surface of each of the electrode plates 212, 214, 222, 224, 232, 634, 642 and 644, to prevent the opposite charges on the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240 from being counteracted even if the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240 meet.

Those skilled in the art will understand that in the above embodiments, the opposite voltages are applied to the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240 to enable the electrostatic actuator 20, but the present invention is not so limited. In some other embodiments of the present invention, the same voltages may be applied to the electrode plates of the four electrode plate pairs 210-240 to enable the electrostatic actuator 20. When the same voltages are applied to the electrode plates of the four electrode plate pairs 210-240, repellent electrostatic force will be generated between the opposite electrode plates of the adjacent electrode plate pairs of the four electrode plate pairs 210-240, the gap distances between adjacent electrode plate pairs of the four electrode plate pairs 210-240 are extended due to the generated repellent electrostatic force and the electrostatic actuator 20 expands.

Those skilled in the art will understand that in the above embodiments, the electrostatic actuator 20 is formed by pilling up the four electrode plate pairs 210-240 together, but the present invention is not so limited. In some other embodiments of the present invention, the electrostatic actuator 20 may be formed by piling up two, three or more four electrode plate pairs together. It is evident that the more the number of electrode plate pairs for forming the electrostatic actuator 20, the larger the stable travel distance achieved by the electrostatic actuator 20 is.

Those skilled in the art will understand that in the above embodiments, the ribbon 200 is insulated, but the present invention is not so limited. In some other embodiments of the present invention, the ribbon 200 may be not insulated. When the ribbon 200 is not insulated, insulated materials are placed between the ribbon 200 and the electrode plates of the electrode plate pairs so that the electrode plates of the electrode plate pairs do not contact the ribbon 200 directly.

Those skilled in the art will understand that various modifications and variations can be made to the above embodiments without departing from the essence of the present invention, and the protection scope of the present invention will be defined by the claims appended.

Claims

1. An electrostatic actuator, comprising:

an elastic ribbon; and

a plurality of electrode plate pairs, each electrode plate pair of which sandwiches the elastic ribbon,

wherein the plurality of electrode plate pairs is piled up into a multi-layer structure through folding of the elastic ribbon.

2. The electrostatic actuator of claim 1, wherein

a gap distance between any two adjacent electrode plate pairs of the plurality of electrode plate pairs is identical.

3. The electrostatic actuator of claim 1 , wherein

the elastic ribbon is insulated.

4. The electrostatic actuator of claim 1, wherein

electrode plates of the plurality of electrode plate pairs have the same shape and dimension.

5. The electrostatic actuator of claim 1, wherein

the plurality of electrode plate pairs is parallel to each other.

6. The electrostatic actuator of claim 1, wherein

the elastic ribbon includes active polymer parts and passive polymer parts connected alternately,

wherein the elastic ribbon is folded at the active polymer parts and each electrode plate pair of the plurality of electrode plate pairs sandwiches the elastic ribbon on one of the passive polymer parts.

7. The electrostatic actuator of claim 6, wherein

the active polymer parts are polyimide hinges that shrink at a prefined temperature or shape-memory polymer elements that actuate with resistive heating.

8. The contactor of claim 1, wherein

a surface of each of electrode plates of the plurality of electrode plate pairs is coated with insulated material.

9. A method for manufacturing an electrostatic actuator, comprising:

installing a plurality of electrode plate pairs on an elastic ribbon at a predefined interval, wherein each electrode plate pair of the plurality of electrode plate pairs sandwiches the elastic ribbon; and

folding the elastic ribbon to pile up the plurality of electrode plate pairs into a multi-layer configuration.

10. The method of claim 9, wherein

the step of installing further includes installing each electrode plate pair of the plurality of electrode plate pairs on one of the passive polymer parts, and

the step of folding further includes coating black ink on one surface of each of the active polymer parts so that surfaces with the black ink of any two adjacent active polymer parts of the active polymer parts are opposite surfaces, and heating the active polymer parts to fold the elastic ribbon at the active polymer parts.

11. The method of claim 9 or 10, wherein

a gap distance between any two adjacent electrode plate pairs of the plurality of electrode plate pairs in the multi-layer configuration is identical.

12. The method of claim 9 or 10, wherein

the elastic ribbon is insulated.

13. The method of claim 9 or 10, wherein

14. The method of claim 9 or 10, wherein

the plurality of electrode plate pairs in the multi-layer configuration is parallel to each other.

15. The contactor of claim 9 or 10, wherein