Electrostatic actuator for providing relative translational motion between components of an electrostatic actuator

Abstract

An electrostatic actuator for translational motion between a stator and a slider in a longitudinal direction (X), comprising a stator drive electrode and a slider drive electrode arranged at respective pitches along the direction (X), the actuator being driven by n power outputs, the stator and / or slider drive electrodes interconnected to n stator and / or slider power buses, the slider and stator buses characterized in that the connections of the n stator buses are configured in a predetermined order, while the connections of the n slider buses are configured in a different predetermined order, and each of the n power outputs is configurable to provide different phases of time-varying power, enabling the generation of a first potential distribution and a second potential distribution moving in opposite directions to each other across the pitch of the stator or slider drive electrode.

Description

Technical Field

[0001] The present invention relates generally to the field of electrostatic motors. More specifically, the present invention relates to linear electrostatic actuators.

Background Art

[0002] Electrostatic motors are known in the art and operate based on the principle of attractive and repulsive forces between electric charges. Early electrostatic motors were generally rotary motors and were used for specific applications such as electrostatic generators.

[0003] Advances in materials science and electronics have led to the development of a new type of electrostatic rotary motor with a planar configuration. Electrostatic micromotors are known that comprise a planar rotor and stator made from thin metal films, wherein the stator comprises both a metal film and an insulating layer which may be, for example, an oxide or a polymer. Other types of micromotors are known in which the rotor comprises an insulator. Such micromotors can rotate at high speed and are widely used in precision instruments and control systems.

[0004] When two electrodes separated by a dielectric material are misaligned and have different electric potentials, an electrostatic attractive force arises, which tends to realign the electrodes and minimize the distance between them. Where a series of electrodes are used, continuous sliding motion can be obtained when driven with an appropriate set of time-varying voltages. This is the basic principle behind linear electrostatic motors.

[0005] It is essential to power known linear motors using a three-phase AC power supply (or sometimes more than three phases), which allows for the generation of two moving potential distributions, the interaction of which fields drives the motor's slider. Known linear electrostatic motors have the problem that designing a suitable means for supplying three-phase AC power to the correct locations within a group of electrodes is sometimes complex. For example, document JP404222471 discloses a system having a bipolar motor with three phases, but it has several drawbacks, including cost, efficiency, speed, and dimensions. The problem of designing a suitable means for getting the power to where it should go is further exacerbated when the AC power supply has more than three phases. The electrodes are usually parallel plates, which generally extend planarly across two dimensions, resulting in a somewhat complex method for bringing the correct electrostatic stimulus to each electrode, usually involving a system of vias and / or bridges. Furthermore, in known electrostatic linear motors, which are generally ribbon-shaped motors, ensuring proper alignment between electrodes and maintaining the correct gap between electrodes during motor operation is also complex. In fact, complex alignment systems must generally be used in modern linear electrostatic motors to ensure that the electrodes remain parallel to each other and maintain the optimal relative position during motor operation.

[0006] Electrostatic motors are highly suitable for applications requiring low energy and high electrical energy density, enabling the fabrication of small and lightweight devices. Other applications where electrostatic linear motors may be used include exoskeletons, artificial muscles, soft robotics, and wearable devices. Therefore, it is desirable to provide elongated electrostatic actuators that overcome some of the shortcomings of known linear electrostatic motors and provide relative translational motion between components. [Overview of the project]

[0007] An object of the present invention is to provide a linear electrostatic motor having a fibrous form factor. Accordingly, a linear electrostatic actuator is disclosed herein, comprising a first elongated, preferably flexible member and a second elongated, preferably flexible member, wherein the first and second members are concentric internal and external fibers designed to slide against each other under electrostatic stimulation. The first member may be referred to as a stator, and the second member may be referred to as a slider or translator.

[0008] According to a first aspect, this specification discloses an electrostatic actuator for converting electrical energy into mechanical force to generate relative translational motion, preferably longitudinally, between a stator and a slider of an actuator. According to one embodiment, the actuator comprises a plurality of electrically isolated stator drive electrodes arranged along the stator, substantially longitudinally, of the actuator, and a plurality of electrically isolated slider drive electrodes arranged along the slider, substantially longitudinally, of the actuator, wherein the stator drive electrodes are electrically isolated from the slider drive electrodes. In the electrostatic actuator, the stator drive electrodes are grouped into n stator buses and interconnected, and the slider drive electrodes are grouped into n slider buses and interconnected. This grouping and interconnection makes it possible to connect each of the n stator buses to one from each of the n power outputs in a predetermined order, while it is also possible to connect each of the n slider buses to one from each of the n power outputs in a different predetermined order. The n power outputs may be supplied from an n-phase power circuit, each of the n power outputs providing a different phase of the AC power supply. The AC power supply can be any multiphase time-varying power supply providing unipolar or bipolar signals such as square waves or rectangular waves, sine waves, or triangular waves. For example, a three-phase unipolar square-wave power supply may be used to enable bidirectional translation between the stator and the slider. As known in the prior art in the field of linear electrostatic motors or translational electrostatic motors, this configuration enables the establishment of a first moving potential distribution across the stator drive electrode and a second moving potential distribution across the slider drive electrode, thereby generating an electrostatic force between the stator and the slider that results in relative translational motion between the stator and the slider. Three phases is the minimum number of phases required to generate relative translational motion in both directions in the longitudinal plane, i.e., bidirectional motion. Two phases are sufficient to generate motion in one direction.

[0009] Advantageously, the stator drive electrode arrangement described above is a three-dimensional arrangement in which multiple stator drive electrodes from each of the n buses are formed along a corresponding one of at least n first stator wires, and each first stator wire for each bus has a three-dimensional configuration of electrically insulated stator windings extending longitudinally around an electrically insulated core containing a dielectric. Similarly, the slider drive electrode arrangement described above is a three-dimensional arrangement in which multiple slider drive electrodes from each of the n buses are formed along a corresponding one of at least n first slider wires, and each first slider wire for each bus has a three-dimensional configuration of electrically insulated slider windings concentric with the first stator winding and extending longitudinally around at least a portion of the first stator winding. Thus, these three-dimensional configurations of the stator windings and slider windings make it possible that the connections between the n power outputs, n stator buses, and n slider buses are essentially achievable at any point along their respective windings. This avoids the need for complex systems of vias or other mechanisms to cross various connections without short-circuiting them.

[0010] Accordingly, according to another aspect, the present invention encompasses a linear electrostatic motor having a stator and a slider, the motor comprising the actuator described above for converting electrical energy into mechanical force to generate relative translational motion between the stator and the slider.

[0011] According to a preferred embodiment, the electrostatic actuator is configured to operate using three-phase electrostatic stimulation, and the actuator comprises three first stator drive electrodes and three first slider drive electrodes, each corresponding to one of the three phases. In this embodiment, bidirectional longitudinal motion may be generated between the stator and slider of the electrostatic actuator.

[0012] In other embodiments, there may be a plurality of first stator drive electrodes and / or a plurality of slider drive electrodes. Different effects can be achieved depending on how the plurality of electrodes are arranged. For example, the wire on which the stator drive electrodes are formed may be wound in a concentric loop around a core, while the wire on which the slider drive electrodes are formed may be wound around the wire on which the stator drive electrodes are formed, thus forming two concentric three-dimensional structures in which the slider wires surround the stator wires. In another variation, there may be a single long stator and a plurality of sliders formed around adjacent sections of the stator. In yet another variation, there may be a plurality of stators aligned in parallel, each stator having at least one slider around it. The sliders may be linked together, or otherwise tied together or coupled together so that their forces can be combined to provide more force to produce movement in the body.

[0013] Any type of wire may be used for the electrodes. According to an advantageous embodiment, a wire having a generally flat profile may be used, thus providing increased force between the stator and the slider. According to a different embodiment, the winding may have an outer shape of cylindrical, square, rectangular, or triangular, and may form, for example, a circular loop, a square loop, or a triangular loop. [Brief explanation of the drawing]

[0014] The inventive concepts described herein will be better understood by the following detailed description and accompanying drawings, which are given as non-limiting examples of embodiments of the inventive concepts. [Figure 1] The principle of operation of a conventional actuator for relative translational motion between a stator and a slider is illustrated. [Figure 2] A schematic diagram of an actuator according to one embodiment of the present invention is shown. [Figure 3a] Figure 2 shows a cross-sectional view of a portion of the actuator at AA. [Figure 3b] Figure 2 shows a cross-sectional view of a part of the actuator at the bracket (BB). [Figure 3c] Figure 3b shows a cross-sectional view of a part of the same actuator, but the actuator has a cylindrical dielectric core made of polymer. [Figure 3d] The images show an unmodulated signal embodiment (left) and a modulated signal embodiment (right) in a custom-made multi-channel board used in a single-pole power supply embodiment. [Figure 4] Figure 2 shows further details of the actuator, revealing a dielectric core, three helically wound stator electrodes embedded in insulating material, and three helically wound slider electrodes embedded in insulating material. [Figure 5a] In some embodiments where both the stator bus and driver bus are connected to the power supply output, the diagram illustrates how electrical connections between the actuator components and the three-phase power supply can be easily made. [Figure 5b] An example of a three-phase AC power supply that may be used to drive an actuator according to an embodiment of the present invention is shown. [Figure 5c] In some embodiments where one of the stator or driver bus is connected to the other and to the power output, an electrical connection may be made between the actuator components and the three-phase power supply. [Figure 6] An example of a wire with a generally flat cross-section, intended for use in helically arranged wires forming the electrodes of an actuator, is shown. [Figure 7] The stator and slider are given a generally cylindrical shape. [Figure 8] The present invention shows an embodiment in which the stator and slider have a generally square or rectangular cross-section. [Figure 9a] Different diagrams of an actuator according to one embodiment of the present invention are shown, comprising two or more sliders, the sliders being coaxial with each other and located around a stator. [Figure 9b]Different views of an actuator according to an embodiment of the present invention are illustrated, the actuator comprising two or more sliders, the sliders being coaxial with each other and arranged around a stator. Figure 9b shows a cross-section of the multi-slider shown in Figure 9a. [Figure 10] An embodiment of the present invention in which the stator has a toroidal shape is illustrated. [Figure 11] A plurality of adjacent sliders are shown arranged around a common stator. [Figure 12] An embodiment of the present invention having a plurality of parallel sliders around a plurality of parallel stators is illustrated. [Figure 13a] A comparison between types of motion achievable with known electrostatic actuators and types of motion achievable using an actuator according to an embodiment of the present invention is illustrated, where Figure 13a represents a known actuator and Figure 13b represents an actuator described in the present specification. [Figure 13b] A comparison between types of motion achievable with known electrostatic actuators and types of motion achievable using an actuator according to an embodiment of the present invention is illustrated, where Figure 13a represents a known actuator and Figure 13b represents an actuator described in the present specification. [Figure 14] An exemplary plot showing how the efficiency and output of an actuator according to an embodiment disclosed herein can vary with input power or speed as a function of load force is shown. MODE FOR CARRYING OUT THE INVENTION

[0015] Embodiments of the present invention may be used to construct a linearly moving electrostatic motor in fiber form. Such a motor comprises two or more concentric fibers configured to slide relative to each other under electrostatic stimulation.

[0016] This application relates, firstly, to an electrostatic actuator (10) whose configuration allows its electrodes to be connected together to the same power source, thereby reducing costs while maintaining efficiency when driven by a voltage signal; secondly, to an electrostatic actuator (10) comprising flexible electrodes; thirdly, to an electrostatic actuator (10) configured to be driven by (or comprising) a unipolar power source; and fourthly, to an electrostatic actuator (10) comprising a modulator for reducing charge injection. This fourth aspect is advantageous in the case of a unipolar power source that would result in large charge injection, but can also be used in the case of a bipolar power source. It should be noted that the first, second, third, and fourth aspects are not mutually exclusive, and therefore the present invention may relate to at least two any combination of these aspects. Furthermore, these aspects are practically independent of each other, and they may each correspond to a single distinct invention, which maintains compatibility with other technical features described in the other aspects. Accordingly, some embodiments of the present invention relate to the arrangement of electrodes and wires therein for enabling efficient force generation with low cost and simplified connections. Such embodiments may include other features described in other embodiments, but preferably include at least the following features: These embodiments relate to an electrostatic actuator (10) for generating substantially longitudinal (X) relative translational motion between a stator (30) of an actuator and a slider of an actuator, wherein a plurality of electrically isolated stator drive electrodes (35) are arranged along the stator at a stator pitch in the substantially longitudinal direction of the actuator, and a plurality of electrically isolated slider drive electrodes are arranged along the slider at a driver pitch in the substantially longitudinal direction of the actuator, the stator drive electrodes (35) are electrically isolated from the slider drive electrodes, the actuator is driven by n power outputs, the stator drive electrodes (35) form a group interconnected to n stator power buses, and the slider drive electrodes form a group interconnected to n slider power buses. The electrostatic actuator (10) The grouping of the sliders and stator buses is such that the connections of n stator buses are configured in a predetermined order, while the connections of n slider buses are configured in a different predetermined order. The three-dimensional configuration of the stator windings and slider windings enables the connection between n power outputs, n stator buses, and n slider buses to be essentially achievable at any point along each winding, Each of the n power outputs is configurable to provide different phases of time-varying power, and the connection is characterized by enabling the generation of a first potential distribution that moves across the pitch of the stator drive electrode and a second potential distribution that moves in the opposite direction to the first potential distribution across the pitch of the slider drive electrode, thereby generating an electrostatic force between the stator and the slider to generate the relative translational motion.

[0017] For example, if each electrode has three wires (n=3), then there are three wires (I, II, III) on the slider and three wires (1, 2, 3) on the stator, and the arrangement of connections allows for motor operation by precise signals (as described herein, which may consist only of simple rectangular pulses) that can associate wire 1 with wire I, wire 2 with wire III, and wire 3 with wire II. For more wires, the associations become more complex, but more efficient and precise signals can be obtained.

[0018] Several embodiments propose new evolutions of power supplies. This section outlines various evolutions and adjustments made to the power supply based on problems identified during observation and measurement. Initially, the inventors used a custom-made multi-channel board capable of generating three-phase and rectangular unipolar unmodulated signals for velocity measurements. Subsequently, for force measurements, the inventors encountered charge injection using insulating polymers fabricated in PVDF (HFP) layers, which led to the transition to the high-voltage amplifier TREK 609-6. Although this amplifier is limited to one channel, it can modulate symmetrical bipolar signals on a single channel, but is insufficient to generate motion requiring three phases. Ultimately, a three-phase modulated signal was required, leading to the development of a second version V2 of the custom-made multi-channel board. This version modulates signals based on the antisymmetric (+ and -) of charge but the symmetry of force.

[0019]

number

[0020] It is characterized by the following, and is represented as states AD, BE, and CF.

[0021] Several embodiments propose novel solutions to the problems of charge injection and polarization in low-frequency signals. After initial force measurements using a first version of a custom-designed power supply, the inventors observed the following phenomenon: when a rectangular unipolar voltage was applied at a frequency of approximately 1 Hz, the force initially increased upon activation of the voltage, then decreased while the voltage remained on, and peaked again when the voltage was turned off. This phenomenon is illustrated in Figure 1, showing two force peaks corresponding to the activation and deactivation of the voltage. This particular measurement was performed using a multi-channel unipolar board of the first version with a fiber length of 1 cm, a voltage of 2.5 kV, a frequency of 0.2 Hz, a phase shift of 120°, and a duty cycle of 50%. Charge injection and polarization were assumed, as in previous experience with PVDF-TrFE-CTFE for electrodeposition, as also noted by other researchers using the same dielectric. Such behavior appears in a dielectric under an electric field in contact with a charged electrode. The following behavior can be observed: a first peak corresponds to an increase in force when the voltage is turned on, then a decrease in force while the voltage is still on (charge injection), and finally a second peak appears when the voltage is turned off. Both the force decrease and the second peak are unsuitable for the device of the present invention, as the maximum force per unit position is required to move the maximum payload, while state switching for motion is also required, and it is necessary to ensure that the electrodes do not generate residual force. Modulation of the signal at frequencies higher than 1 Hz prevents charge injection and polarization of the PVDF. The inventors also determined a time constant τ=RC=1ms on the voltage graph. Assuming a 5MΩ resistor is used between the power supply and the motor, and the motor resistance is less than 5 ohms (negligible in comparison), the capacitance of the motor is calculated to be C=0.2nF, and theoretically the operating frequency is limited to a maximum of 1kHz.

[0022] Several embodiments are designed to improve the number of use cases for the actuator. Such embodiments relate to an electrostatic actuator (10) for generating substantially longitudinal (X) relative translational motion between an actuator stator (30) and an actuator slider, wherein a plurality of electrically isolated stator drive electrodes (35) are arranged along the stator at a stator pitch generally in the longitudinal direction of the actuator, and a plurality of electrically isolated slider drive electrodes are arranged along the slider at a driver pitch generally in the longitudinal direction of the actuator, the stator drive electrodes (35) are electrically isolated from the slider drive electrodes, the actuator is driven by n power outputs, the stator drive electrodes (35) form a group interconnected to n stator power buses, and the slider drive electrodes form a group interconnected to n slider power buses, and such an electrostatic actuator (10) is characterized in that the stator drive electrodes (35) and the slider drive electrodes (35) are flexible to allow the actuator to be bent without plastic deformation. In this specification, the term “flexibility” refers to the ability of a fiber (i.e., electrode) to bend and have elastic deformation, as opposed to stiffness, which refers to an element that is more likely to break or undergo plastic deformation. Flexibility can be defined, for example, by the radius of curvature. Furthermore, the flexibility of an element depends on the material, but also on the size of such an element, and, for example, in some embodiments of the present invention, on the three-dimensional layout of a device having a wire winding. Thus, the flexibility of a fiber in this application can be defined in relation to the size of the three-dimensional layout, such as, for example, the outer diameter of the external electrode (or “fiber”) containing the wound wire. An element is considered flexible in this application if its minimum radius of curvature (without breakage or plastic deformation) is at least greater than the diameter of the external electrode. In various embodiments, the fiber (i.e., electrode) is so flexible that it has a radius of curvature as small as the diameter of the external fiber (a radius of curvature on the order of a few millimeters for a wire with a diameter of several hundred microns).Furthermore, such a three-dimensional layout with wound wires forms a spring-like arrangement that is more resistant to deformation and can withstand bending with a smaller radius of curvature without plastic deformation.

[0023] Some embodiments use frequency modulation with one phase. Since custom-made power supplies can only generate unipolar signals, a high-voltage amplifier TREK 609E-6 was used to modulate the signal with a bipolar voltage waveform. In some experiments, a square unipolar signal was replaced with a modulated bipolar square waveform switching from +2.5kV to -2.5kV. For demonstration purposes, only a modulation frequency of 4Hz was used (however, frequency sweeps are possible to determine the optimal modulation frequency). This figure shows that the measured force increases when the voltage is on, oscillates around an average force of 33mN at the modulation frequency, and returns to 0mN when the voltage is turned off. The observation demonstrates that by using a modulated signal from a high-voltage source such as TREK, each state (A, B, or C) can be maintained at a specific position, albeit not sequentially, since TREK has only one output. This signal and power setup can be employed to characterize force measurements, as external fibers can be clamped and each state can be activated independently, albeit not sequentially. Nevertheless, modulation of the three phases is necessary to facilitate payload measurement and to generate the desired power output while sequentially switching between states A, B, and C.

[0024] Conversely, some embodiments use modulation of a square unipolar three-phase signal. To generate a three-phase signal with a modulated signal using only unipolar channels, this application proposes devising a method for switching the potential of the electrodes without changing the generated electrostatic force. In Figure 1, the left side shows the old signal generated by a first version of the multi-channel board (unmodulated). Subsequently, the sequence A>B>C>D(A)>E(B)>F(C) was generated, corresponding to 6 steps per period for each change in voltage in one of the three phases. Taking states A and D as examples, the inventors noticed that states A and D are antisymmetric with respect to electrode potential: that is, the high-voltage electrode and the grounded electrode are opposite, but the static voltage remains constant. This means that by alternating between A and D, the potential of each electrode is switched at the modulation frequency, so a composite state AD can be generated that produces the same force as A or D, while preventing charge injection and polarization. By applying the same principle to BE and CF, the new signal shown on the right side of Figure 3d can be generated. This new signal has a period of three new steps AD>BE>CF, which means that for a constant speed:

[0025]

number

[0026] Let N be the number of steps and T be the period.

[0027]

number

[0028] To maintain a constant speed between the old and new sequences, it is necessary to generate frequencies for the AD, BE, and CF sequences that are twice as high as the frequencies required to generate A>B>C>D(A)>E(B)>F(C).

[0029] Figure 1 shows a schematic cross-sectional view of a known electrostatic actuator for providing relative translational motion between a stator and a slider using a three-phase AC power supply. This type of actuator is defined by the preamble of the main independent claims of the present invention.

[0030] Figure 2 shows a diagram of an electrostatic actuator according to one embodiment of the present invention, Figure 3a shows a detail of a cross-section through AA, and Figure 3b shows a cross-section through BB. The actuator comprises an outer fiber and an inner fiber that slide against each other when driven by a suitable AC multiphase electrostatic stimulus. For each phase of the power supply, the inner fiber, i.e., the stator, has a number of windings of wire or other conductors containing a number of stator electrodes, and the outer fiber, i.e., the slider, has a number of windings of another wire or conductor containing a number of slider electrodes. In the case of a three-phase power supply, the stator has a number of stator electrodes and three helically wound stator wires, and the slider has a number of stator electrodes and three helically wound slider wires.

[0031] The three stator wires, like the three slider wires, are electrically insulated from each other, and all stator wires are electrically insulated from the slider wires. According to one embodiment, the stator wires may be wound around a core of dielectric material. The core may be air or another gas, or a liquid, or a physical core made from a dielectric material such as a polymer. According to one embodiment, the stator wires may simply be embedded within fibers of a polymer dielectric material, thus ensuring electrical insulation from each other and from the slider wires. The slider wires may be wound around the stator so as to allow the slider to slide over the stator. Generally, the slider is significantly shorter in length than the stator, but in some embodiments, both the slider and stator may be substantially the same length, which may, in some cases, be hundreds of times longer than the thickness or diameter of the stator or slider. The slider wires may be embedded in polymer fibers to provide sufficient insulation between the slider windings and between the stator windings and the slider windings. The stator and slider may be substantially concentric.

[0032] Other numbers of stator and slider wires are also possible, such as two or four or more. However, three electrodes are the minimum number that allows for bidirectional translation of the actuator components. According to one embodiment, the windings are in a helical form. In a preferred embodiment, though not required, the pitch of the stator windings substantially matches the pitch of the slider windings.

[0033] Each stator wire receives a different phase of the multiphase AC power supply, and so do each slider wires. In a preferred embodiment, the order in which the three power phases are supplied to the stator wires differs from the order in which the power phases are supplied to the slider wires, thus setting the static force that causes relative motion between the stator and the slider.

[0034] Figure 3b shows a linear electrostatic motor exhibiting a fiber configuration including an optional core filament according to an embodiment of the present invention. One conductive wire, each containing a stator electrode, is wound around the core for each phase. The resulting structure can be described in this example as an internal fiber comprising three conductive wires, each having multiple stator electrodes. One conductive wire can be wound around a portion of the stator for each phase to form a slider, each wire containing a slider electrode. According to one embodiment, insulation between windings can be achieved by alternately winding insulating wires between each of the conductive wires. According to another embodiment, the wires may be coated with an insulator. According to one embodiment, the conductive wires are made of copper and embedded within a polymer fiber. In another embodiment, the wires may be conductive wires covered with a thin insulator and wound around the core. The resulting structure of conductive wires wound around an internal fiber to allow windings to slide on the internal fiber may, in this embodiment as well, be called an external fiber comprising three conductive wires, each having multiple slider electrodes. By setting a first moving potential distribution on the stator electrode using a three-phase power supply appropriately connected to the three conductive wires of the internal fiber, and setting a second moving potential distribution on the slider electrode using different phases of the power supply appropriately connected to the three conductive wires of the external fiber, it is possible to generate an electrostatic force that moves the slider relative to the stator, i.e., slides the external fiber on the concentric internal fiber in the direction of the two fiber axes.

[0035] Actuators as described above are readily available today because the precision required to achieve the appropriate winding pitch for creating actuating actuators with such fiber morphology is now available in the industry. Since concentric fibers self-align, there is no problem with having to control the alignment of electrodes. In a preferred embodiment, the internal winding pitch matches the external pitch. If the internal and external winding pitches do not match, force loss may occur, which can be substantial. However, in some cases, such loss is acceptable, and therefore, in certain embodiments, the need for a precise match between the internal and external pitches may not be essential.

[0036] The wires may be wound and covered with insulating material. According to one embodiment, the actuator comprises an inner fiber having a plurality of helically wound wires and an outer fiber having a plurality of helically wound wires. The outer fiber is configured to slide on the inner fiber. When a suitable voltage sequence is applied to the inner and outer wires, the two fibers move relative to each other. The direction and speed of the movement can be controlled by controlling the stimulus.

[0037] The AA section in Figure 4 shows multiple wires wrapped around both the inner and outer fibers. In this embodiment, three wires are used for both the inner and outer fibers, but the number of wires is not limited to three.

[0038] In this configuration, in contrast to planar devices known in the prior art, each electrode (in this case, a wire) is continuous, thus facilitating connection to a suitable power source. For example, in the schematic diagram, the electrode labeled "1" represents only one conductive wire.

[0039] The same process can be used to wrap and encapsulate both the inner and outer fibers. The core filament may be removed from the outer fibers and replaced by the inner fibers.

[0040] The fibers may be flexible. The windings of the two fibers should have the same pitch, but as mentioned above, precise pitch matching between the inner and outer windings is not essential if the associated power loss is acceptable. The windings are easily achieved using a machine that winds wire around each fiber at a predetermined rotational speed.

[0041] To increase efficiency, it is preferable to minimize the distance between the inner and outer windings, but a trade-off is made between reducing friction between the two fibers and increasing the force that can be provided by the actuator. Voltage level also plays a role, as does weight. Dimensions also play a role; as dimensions increase, an increase in voltage is required. The voltage-to-size ratio limit is reached when the required voltage is sufficient to cause dielectric breakdown of the air. An exemplary spacing between the inner and outer fibers is 100 μm to 200 μm, i.e., 200 μm to 400 μm assuming gaps on both sides.

[0042] Any conductor may be used, and any insulator may be used as long as it has sufficient resistivity compared to the conductor and a sufficiently high dielectric breakdown field. In a preferred embodiment, copper is used as the conductor and nylon is used as the insulator. The insulator may be an elastomer as long as it is non-conductive. The insulator should preferably have a high dielectric constant (i.e., a large dielectric constant). Insulating oil may be used between the internal and external fibers to reduce friction between the moving parts.

[0043] Embodiments of the present invention may feature a non-cylindrical wire. For example, a wire having a square cross-section may be wound around a triangular core, a cylindrical core, or a square / triangular core, etc. In preferred embodiments, the wire has a generally flat cross-section. Generally flat may mean, for example, an oblong, elliptical, square, or rectangular cross-section.

[0044] According to one embodiment, the winding is achieved using scattered copper wires and nylon wires, for example, 200 μm copper and 100 μm nylon.

[0045] Miniaturization is possible: Miniaturization allows for increased force, as well as a reduction in the size of the corresponding support and drive circuits, meaning that the actuator according to the embodiment of the present invention can be made lighter so that it can be easily installed on a drone.

[0046] Two phases are sufficient for a moving actuator, but three phases are preferable to enable bidirectional translation. More than three phases, such as four, are also possible.

[0047] Figure 5b shows an electrostatic stimulus that may be used in embodiments described herein, illustrating how easy it is to achieve connection from an AC power source to different electrodes of an actuator. Many different types of drive waveforms (electrostatic stimuli) are possible. In the case of a unipolar voltage stimulus with fibers and three phases, the figure shows that electrical connection of the fibers to the power source is easily achievable. As shown in Figure 5b, once a suitable multiphase electric drive is supplied to both fibers, they slide against each other. The figure also shows a voltage-versus-time plot for each wire, illustrating how a traveling wave can be generated using a unipolar square signal. Bipolar signals are also possible. Such unipolar stimuli have the advantage of reducing the cost of the power source compared to bipolar stimuli, which require precise placement to generate voltages of opposite values. However, such advantages of unipolar power sources can induce disadvantages such as charge injection. Charge injection is a complex mechanism in which charge accumulates in a material that is subjected to current. When the voltage is on and the frequency is sufficiently low (about 1 Hz), it can be observed that the force decreases significantly while the voltage is high and constant. A common explanation is that electric charge accumulates between the inner and outer fibers and is located at the interface between the insulator and the lubricant (e.g., the insulating layer PVDF (HFP) and silicone oil). The following solutions have been proposed to prevent charge injection: - By using better dielectric constant matching between the insulator and the oil, for example, using paraffin oil, charge injection can be "easily" prevented, and thus unmodulated signals can be used. By using a motor at a frequency higher than -20Hz, the frequency can be made high enough to prevent charge injection. - Use a bipolar three-phase signal so that opposite charges cancel each other out.

[0048] This application proposes other solutions, such as driving a motor using a single-pole signal, preferably with a specific modulation of this signal. These solutions are convenient because they enable the following: - Use a standard lubricant such as silicone oil with high dielectric strength and low viscosity to insulate the fibers and reduce friction. - Use a three-phase single-pole power supply to limit costs compared to a bipolar signal.

[0049] Such unipolar motors simplify connections because, in addition to using only two potentials (+ and ground), they can connect the inner and outer fiber electrodes and use only three "wires" to supply power to the motor. Conversely, conventional techniques, such as those described in reference JP404222471, require different signals for the inner and outer electrodes, which means that two different signal generators (one for the inner and one for the outer) are needed, making it impossible to connect the signals and electrodes necessary to drive the motor, depending on the motor's structure. Therefore, such solutions result in a significant increase in the motor's cost.

[0050] Modulation offers the advantage of reducing charge injection and improving performance, not only in unipolar embodiments but also in bipolar modifications.

[0051] As the frequency of the three-phase electrostatic stimulation increases, the speed of the sliding motion increases proportionally, demonstrating that the motor's operation is primarily a result of electrostatic force. Furthermore, it is noteworthy that the alignment structure required in conventional linear electrostatic motors is unnecessary. As mentioned above, connection to the power supply is remarkably simple.

[0052] The actuators according to the embodiments disclosed herein enable substantial relative translational motion between the stator fibers and slider fibers, but torsional forces can also be present due to the helical configuration of each winding, and therefore, in embodiments in which the stator and slider fibers have a substantially cylindrical cross-section, relative torsional motion can also be present to some extent, as well as the desired relative translational motion.

[0053] Figure 13a shows the types of relative motion between the stator and rotor of an electrostatic rotary motor, or between the stator and slider of an electrostatic linear motor, that were achievable using known techniques, and Figure 13b shows the type of coaxial translation achievable using the electrostatic linear motor in which embodiments of the present invention are deployed. As illustrated, known linear electrostatic motors were unable to achieve coaxial translation and were only capable of coaxial rotation, planar rotation, or planar translation. The electrostatic motor in which embodiments of the present invention are deployed makes it possible to achieve coaxial translation of fibrous components and provides several advantages over known planar designs of electrostatic motors. Such advantages include: • Fibers are flexible, allowing for complex bending, and therefore can generate forces and displacements in any complex shape (such as the human body). • Coaxial design allows for much simpler electrical connections to three-phase or more-phase power supplies compared to planar designs. The outer fibers can rotate without hindering the desired linear motion. Unlike planar systems, coaxial fibers do not require an alignment system to maintain the parallelism needed during movement. The geometric shape of the fibers allows for easy integration into clothing through techniques such as weaving and knitting. The geometric shape of the fibers makes it easy to configure multiple actuators in parallel, similar to muscle fiber bundles.

[0054] In some embodiments of the actuator, at least one further slider is mounted in series with a first slider on the same stator, and the n power buses interconnect the further sliders by connecting one of the n further slider wires in one slider or one of the first slider wires to a corresponding one of the n further slider wires in another slider, while the first slider comprises one of the n first slider wires connected to one of the n power outputs.

[0055] In some embodiments of the actuator, the actuator comprises a plurality of sliders and stators mounted in parallel, and the n power buses interconnect one of the first or further sliders to further sliders by: - One of at least n first slider wires or further slider wires in one slider is connected to a corresponding one of at least n further slider wires in another slider, while the first slider is connected to one of n power outputs. - One of at least n first slider wires or further slider wires in one stator is connected to a corresponding one of at least n further stator wires in another stator, while the first stator is connected to one of n power outputs.

[0056] Such groups of sliders, particularly in the case of parallel sliders and stators forming bundles of motor fibers, enable an efficient increase in motor strength.

[0057] From Figures 4 and 5a, it is clear that embodiments of the present invention enable extremely simple connections between each electrode group, onto their corresponding buses, and then to the appropriate phases of the power supply. In fact, each of the three stator wires shown in Figure 4 forms a three-dimensional shape around the core of the actuator, and at the same time constitutes multiple stator drive electrodes and the interconnections necessary to bring all of these electrodes onto a single bus connected to one phase of the power supply. Thus, the three wires form three electrode groups and their buses, each connected to each phase of the power supply. Similarly, each slider wire, which forms a three-dimensional shape, in this case a substantially helical shape, around the insulator for the stator wires, at the same time constitutes multiple slider drive electrodes and the interconnections necessary to bring all of the slider drive electrodes in one phase together onto a bus for connection to each phase of the power supply. It can even be said that the helical shape itself is the bus, and therefore the bus can be connected to each phase of the power supply at any point along its length in a very convenient manner. Figure 5b shows an example of a three-phase power supply that can be used to operate an actuator according to one embodiment. In this embodiment shown in Figures 5a and 5b, phase 1 is applied to the first wire in the outer fiber and the first wire in the inner fiber, and phase 1 is applied to 2 * Phase 2, which delays the phase by π / 3 radians, is applied to the second wire of the outer fiber and the third wire of the inner fiber, and phase 1 is delayed by 2. * A phase advance of π / 3 radians, phase 3, is applied to the third wire of the outer fiber and the second wire of the inner fiber.

[0058] Figure 6 shows an embodiment in which the wires in the internal fibers and the wires in the external fibers have a generally flat cross-section, for example, a square or rectangular cross-section. This configuration has the advantage of being able to increase the electrostatic force. Figures 7 and 8 show different cross-sections that can be given to the fibers themselves according to different embodiments. Figures 9a and 9b show embodiments having more than two concentric fibers. In this embodiment, it can be said that the stator is composed of internal or core fibers having a first slider formed by central concentric fibers around the internal fibers and a second slider formed by external concentric fibers around at least a portion of the first two. Figure 10 shows a stator having a toroidal shape. Figure 11 shows a single stator having three series sliders.

[0059] According to some embodiments, the electrodes of the stator are formed on a set of wires wound in a substantially elongated helical structure, and the electrodes on the slider are also formed on a set of wires wound in a substantially elongated helical structure. The slider or stator may be the inner electrodes, while the other is the outer electrode extending around at least a portion of the inner electrodes, thus resulting in an innovative concentric fiber structure for the electrostatic linear actuator according to some embodiments of the present invention. Thus, these embodiments are not affected by the problems faced by known electrostatic linear actuators, which generally require some alignment means to maintain their electrodes in the required relative positions to each other during the operation of the actuator, because proper alignment of the electrodes is achieved automatically thanks to the concentric fiber architecture of the actuator. Therefore, it can be said that the actuators according to embodiments of the present invention are self-aligning. The terms “electrode,” “wire,” and “bus” (actually “power bus” or “rail”) are used herein to functionally distinguish the different parts of the actuator, because the wire (having any shape of its cross-section) is wound to form electrodes connected to a power source and / or another electrode (stator / slider). However, these functional parts may also be formed by the same (n) wires from the power source to the end of the actuator, and these terms do not imply any limitation.

[0060] Embodiments of the present invention using three-phase electrostatic stimulation provide a pair of moving potential distributions across each of three pairs of electrodes according to a three-phase AC power supply used to provide the stimulation, thereby generating an electric field interaction that provides relative translational motion between a pair of coaxial fibers around which the electrodes are wound.

[0061] In a preferred embodiment of the present invention, the windings within the inner and outer fibers are substantially helical in form, i.e., they have a three-dimensional arrangement that appears to form concentric helical winding groups (typically three wires in one group) with one in the other. Connections to each wire within one fiber can be made relative to the phase of the power supply, while connections to each wire within another fiber can be made either directly relative to the appropriate phase of the power supply, depending on the required phase, or indirectly by connecting to one of the appropriate wires from the first fiber. To generate motion between the stator and the slider, the connections must result in opposite propagating potential distributions across the opposing electrode groups. The correct selection of connections depends on whether the windings form a clockwise or counterclockwise helix, and the order of connections in the inner fiber differs from the order of connections in the outer fiber.

[0062] To operate the actuator according to the embodiments described herein, the static voltage must exceed both the static friction and weight of the internal or external fibers of the actuator. To ensure this, the voltage must be adjusted up or down based on the breakdown limit and the power supply or battery requirements for using the fibers. Furthermore, considering the dimensions of the various components of the electrostatic linear actuator according to the embodiments described herein, the dimensions are primarily constrained by the distance between the internal and external fibers. This distance, denoted as "d", must be greater than zero and must adhere to a voltage-to-distance ratio higher than the dielectric breakdown limit of the insulator between the internal and external fibers. For example, assuming the electric field value between the internal and external fibers is between 0.1 V / μm and 1 kV / μm, the electrostatic force is expressed by the following equation: Force=12.ε0.εr.E2.Surface, Here, ε0 is the permittivity of vacuum, εr is the permittivity of the insulating material between the fibers (this can be a composite material of multiple materials having collective permittivity), E is the aforementioned electric field, and "surface" is the interaction surface between the internal and external fibers. Then, whether internal or external, the motor speed depends on various factors such as frequency, payload charge, and required force. A standard plot used to characterize a motor is input power (power) against load force, output power (force). * Speed, velocity, and efficiency can be characterized (in Figure 14, P-in, P-out, Spd, and Eff, respectively). These properties vary significantly depending on the fiber dimensions and can potentially vary by several orders of magnitude.

Claims

1. An electrostatic actuator (10) for generating substantially longitudinal (X) relative translational motion between a stator (30) of an actuator and a slider of the actuator, wherein a plurality of electrically isolated stator drive electrodes (35) are arranged along the stator at a stator pitch in approximately the X direction, a plurality of electrically isolated slider drive electrodes (25) are arranged along the slider at a driver pitch in approximately the X direction, the stator drive electrodes (35) are electrically isolated from the slider drive electrodes (25), the actuator is driven by n power outputs, the stator drive electrodes (35) form a group interconnected to n stator power buses, and the slider drive electrodes (25) form a group interconnected to n slider power buses. The electrostatic actuator (10) - The grouping of the sliders and stator buses is such that the connections of the n stator buses are configured in a predetermined order, while the connections of the n slider buses are configured in a different predetermined order. - The three-dimensional configuration of the stator windings and slider windings enables the connection between the n power outputs, the n stator buses, and the n slider buses to be essentially achievable at any point along each winding, An electrostatic actuator (10) characterized in that each of the n power outputs can be configured to provide different phases of time-varying power, and the connection enables the generation of a first potential distribution moving across the pitch of the stator drive electrode and a second potential distribution moving in the opposite direction to the first potential distribution across the pitch of the slider drive electrode, thereby generating an electrostatic force between the stator and the slider to generate the relative translational motion.

2. The electrostatic actuator according to claim 1, wherein the configuration of the connection is such that both the stator bus and the driver bus are connected to the power output, or one of the stator bus or the driver bus is connected to the other and the power output.

3. The electrostatic actuator according to claim 1 or 2, further comprising at least one further slider (21, 204, 205, 206) having at least n further slider wires (a, b, c), one for each of the n power buses, and further plurality of slider drive electrodes having further slider wires having a three-dimensional configuration of electrically insulated slider windings extending in the longitudinal direction, either around adjacent portions of the stator winding (30) formed by the first stator wire, or around at least a portion of the slider winding formed by the first slider wire.

4. The electrostatic actuator according to claim 3, wherein at least one further slider is mounted in series with a first slider on the same stator, and the n power buses interconnect the further sliders by connecting one of the n further slider wires in one slider or from the first slider wire to a corresponding one of the n further slider wires in another slider, while the first slider comprises one of the n first slider wires connected to one of the n power outputs.

5. The electrostatic actuator according to claims 1 to 4, wherein the plurality of stator drive electrodes (35) are formed along a corresponding one from at least n first stator wires (1, 2, 3), and each first stator wire connected to each of the n buses has a three-dimensional configuration of electrically insulated stator windings extending longitudinally around an electrically insulated core including a dielectric, and the plurality of slider drive electrodes from each of the n buses are formed along a corresponding one from at least n first slider wires (I, II, III), and for each bus, each first slider wire has a three-dimensional configuration of electrically insulated slider windings concentric with the first stator windings and extending longitudinally around at least a portion of the first stator windings.

6. An electrostatic actuator according to any one of claims 1 to 5, comprising a plurality of parallel sliders (201, 202, 203) and a corresponding plurality of parallel stators (301, 302, 303).

7. The electrostatic actuator according to claim 6, wherein the plurality of sliders are physically coupled together so that they move as a single unit.

8. If the actuator comprises a plurality of sliders and stators mounted in parallel, the n power buses are: - One of at least n first slider wires or further slider wires in one slider is connected to a corresponding one of at least n further slider wires in another slider, while the first slider is connected to one of n power outputs, - One of at least n first slider wires or further slider wires in one stator is connected to a corresponding one of at least n further stator wires in another stator, while the first stator is connected to one of n power outputs, The electrostatic actuator according to claim 5 or 6, wherein the first slider or one of the further sliders is interconnected to the further slider.

9. The electrostatic actuator according to any one of claims 1 to 8, wherein the stator has a toroidal shape.

10. The electrostatic actuator according to any one of claims 1 to 9, wherein the stator wire and the slider wire have a substantially circular cross-section or a generally flat cross-section.

11. The electrostatic actuator according to any one of claims 1 to 10, wherein the winding has a substantially helical shape.

12. The electrostatic actuator according to any one of claims 1 to 11, wherein all of the windings have substantially equal winding pitches.

13. The actuator according to any one of claims 1 to 12, wherein n has a value of at least 3, and thereby the actuator is a bidirectional actuator.

14. The actuator according to any one of claims 1 to 13, wherein the dielectric contained in the electrically insulated core includes a gas such as air, a liquid, or a polymer.

15. The actuator according to any one of claims 1 to 14, further comprising a lubricant between either the stator winding or the slider winding.

16. The actuator according to any one of claims 1 to 15, wherein the stator and the slider are flexible so that the actuator can be bent without plastic deformation.

17. The actuator according to any one of claims 1 to 16, wherein the stator is substantially longer than the slider.

18. A linear electrostatic motor comprising the actuator described in any one of claims 1 to 16.

19. The linear electrostatic motor according to claim 17, further comprising a power supply configured to generate n phase time-varying powers to drive the n buses, generate a first moving potential distribution on the stator drive electrode (35), and generate a second moving potential distribution on the slider drive electrode, thereby generating an electrostatic force between the stator and the slider to generate the relative translational motion.

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