Micro-electromechanical system (MEMS) actuator with magnetic locking and methods of making and using the same

Abstract

The present application provides an electromechanical actuator comprising: a stator assembly having a chamber defined through the stator assembly along a central longitudinal axis portion; and a plunger assembly disposed in the chamber and movable in operation between different positions along the central longitudinal axis. The stator assembly may include a pair of contacts having an opening therebetween and ferromagnetic layers of three in a group with a coil therebetween. The plunger assembly may include a magnet. When an electric current is applied to the coil, the ferromagnetic layers of three as a group are magnetically polarized, thereby governing the movement of the plunger assembly by magnetically attracting or repelling magnets included in the magnetic plunger assembly. The plunger assembly may be stabilized by a flexure that flexibly connects the stator assembly and the plunger assembly.

Description

TECHNICAL FIELD

[0001] Various embodiments relate to electromechanical actuators, and more particularly to actuators designed for applications requiring fast motion, bi-stable latching, large latching force relative to their size, and / or large travel, as well as methods of manufacturing and using such electromechanical actuators. BACKGROUND

[0002] An electromechanical actuator is a device that converts electric current into mechanical motion. A solenoid actuator is a particular type of electromechanical actuator that provides linear motion between two positions. Solenoid actuators are used in a variety of applications, including opening and closing electrical contacts in relays, opening and closing valves, latching and unlatching doors or hatches. Solenoid actuators are constructed using a wire coil wound on an open cavity or ferromagnetic core. A ferromagnetic armature (also referred to as a "plunger" or "piston") can be located inside the coil, or can be axially located at one end of the coil. Electric current flowing through the coil creates a magnetic field that causes the solenoid actuator's armature to "suck in." When the current stops, a spring returns the armature to its unenergized position. Some solenoid actuators are bi-stable (or "latching"). In such solenoid actuators, the plunger is held at either end of travel by a magnet or mechanical restraint. In the case of a bi-stable solenoid actuator, electric current flowing through the coil can be delivered in both directions to move the plunger from one end of the solenoid actuator to the other. BRIEF DESCRIPTION OF DRAWINGS

[0003] The patent or application contains at least one drawing executed in color. Copies of this patent or patent application with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0004] Figure 1 includes a schematic diagram of a solenoid or actuator having a traditional electromagnetic form.

[0005] Figure 2A includes a cross-sectional view of the layers of an actuator according to various embodiments of the disclosure.

[0006] Figures 2B-2C shows Figure 2A The layers of the illustrated electromechanical actuator generally correspond to one of two "stacks," namely a static stack (also referred to as a "stator assembly") or an actuatable stack (also referred to as a "rotor assembly" or "plunger assembly").

[0007] Figure 3 includes a simplified schematic diagram of the electromechanical actuator latching behavior caused by the magnetic circuit of the "open position" and "closed position."

[0008] Figure 4 includes a schematic diagram showing that applying electric current through the coil will result in an approximately constant magnetic force being applied to the plunger.

[0009] Figures 5A-5E Magnetic flux is shown as the plunger assembly moves from the first position to the second position and then back to the first position.

[0010] Figure 6 Including a perspective cross-sectional view showing how the flexure connected to the plunger assembly constrains the motion of the plunger assembly relative to the stator assembly.

[0011] Figure 7 Including a cross-sectional schematic of the plunger assembly, the contact assembly, and the stator assembly.

[0012] Figure 8 Including a cross-sectional view of the electromechanical actuator and a possible assembly sequence schematic.

[0013] Figure 9 Including a high-level flowchart for manufacturing the electromechanical actuator.

[0014] The embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. While various embodiments have been depicted and described, alternative embodiments can be employed without departing from the spirit or intent of the technology. Accordingly, the technology is not intended to be limited to the specific embodiments illustrated in the figures. DETAILED DESCRIPTION

[0015] Electromechanical actuators have historically been used in many contexts. Many devices that require electrically controlled motion can be driven by electromechanical actuators. Examples of such devices include valves, haptic feedback devices, and electromechanical relays. Low power devices, such as microprocessors, can drive such actuators to activate a switch (relay) to control an electrical load beyond their direct driving capabilities. Electromechanical actuators can also be used to drive valves, optical elements (such as mirrors or lenses), mechanical or electrical tuning elements, fluid pressure modulators or pumps, and many other useful loads in applications.

[0016] Figure 1 Including a schematic of a solenoid or actuator with a traditional electromagnetic form. The traditional electromagnetic form includes a control coil (102) wound on a ferromagnetic core (104). Application of current through the control coil (102) creates a magnetic field whose direction is generally parallel to the axis of the coil (102). This magnetic field attracts the upper contact of the two contacts (108). The upper contact moves downward until it contacts the lower contact (108). This closes the switch, allowing current to flow from the power source to the load. When the current through the control coil (102) is blocked by opening the control switch (106), the upper contact (108) returns to the neutral, open position by spring force.

[0017] Typically, conventional electromechanical actuators are at least a few centimeters in length and width. Their construction requires winding coils that must be formed using a winding machine. The winding of the coils adds complexity to the production of such actuators, and thus increases cost. In contrast, the electromechanical actuators presented herein allow the use of planar circuitry, reducing the complexity of forming the coils and resulting in devices that are much smaller, on the order of 1 millimeter (mm) x 6 mm x 6 mm or less in size. This makes the resulting devices useful for applications that require small size.

[0018] Conventional solenoid actuators typically do not latch in place at one end of the stroke, even in implementations where latching is possible, latching is typically achieved mechanically. Mechanical latching adds an active component to the design, increasing cost and decreasing reliability. The electromechanical actuators presented herein provide magnetic latching at each end of their stroke as a function of their design, and without the need for additional components. Magnetic latching is entirely passive, requiring no external energy to hold the plunger at either end of the stroke.

[0019] Terminology

[0020] Definitions for terms, abbreviations, and phrases used throughout the application are given below.

[0021] References in the specification to "one embodiment" or "some embodiments" mean that a described feature is contained in at least one embodiment of the technology. The appearances of such phrases in various places in the specification are not necessarily referring to the same embodiment, nor are they necessarily mutually exclusive alternatives.

[0022] The terms "comprise," "comprising," and "comprises," and "comprised of" when used in this specification, are each taken to specify the presence of stated features, integers, steps, or components but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. The term "based on" is used to describe one or more factor to which determination of one or more other variables is based, at least in some measure. Thus, "based on" is not exhaustive and is used in the sense of "based, at least in part, on."

[0023] The terms "connected," "coupled," and any variant of either term mean any connection or coupling, either direct or indirect, between two or more elements. Such connection or coupling can be physical, logical, or a combination of both. For example, objects can be electrically connected or communicatively connected to one another even though they do not share a physical connection.

[0024] Overview of electromechanical actuator

[0025] At a high level, the electromechanical actuators described herein are laminated devices, typically manufactured by cutting thin sheets of material and then bonding those sheets into a stack, as discussed further below. Through successive iterations of cutting / bonding, structures that collectively make up the electromechanical actuators can be placed coplanar to one another in almost any configuration.

[0026] Figure 2A A cross-sectional view of the layers comprising the electromechanical actuator 200 according to various embodiments of the present disclosure. Also shown is a load 218 that is to be moved by the electromechanical actuator 200. Figures 2B-2C The layers of the electromechanical actuator 200 are shown generally how they correspond to one of two "stacks," namely a static stack 232 (also referred to as a "static assembly," a "stator assembly," or simply a "stator") or an actuatable stack 234 (also referred to as an "actuatable assembly," a "rotor assembly," a "plunger assembly," or a "plunger"). As discussed further below, the plunger assembly 234 is vertically displaceable within the stator assembly 232 to controllably move the load 218.

[0027] Referring again to Figure 2A , the stator assembly 232 represents a collection of layers having a cavity 236 that is partially defined along a central longitudinal axis 238 through the stator assembly. The central longitudinal axis 238 can generally bisect the width of the electromechanical actuator 200. The base plate 202 is the bottom-most layer of the stator assembly 232. The base plate 202 can be a small piece of insulating material on which functional components (e.g., relays or valves) are fabricated to complete the electromechanical device. The insulating material can be ceramic or glass, for example. Insulation is not always necessary (e.g., if the electromechanical actuator 200 forms part of an electrical switch, insulation can be helpful). Thus, the base plate 202 can also be constructed of a non-insulating material on which functional components are fabricated to complete the electromechanical device. Some embodiments can not include a base plate 202 at all, in which case the load stops 204A-204B can be the bottom-most layers of the electromechanical actuator 200.

[0028] In terms of "footprint," it is generally desirable to make the electromechanical actuator 200 as small as possible, within the limits set by current density. Cost and magnetic performance often scale favorably with size reduction. For example, the actuation force can be proportional to the square root of the moving magnet mass and the square root of the power dissipation of the electromechanical actuator 200. Typically, the thickness of the substrate 202 can be less than 4 millimeters (preferably less than 3 mm thick). The thickness of the substrate 202 can be critical to the operation of the electromechanical device, and thus can not be heavily dependent on the intended application of the electromechanical actuator 200. The shape, length, and width of the substrate 202 can vary depending on the intended application of the electromechanical device 200. However, in some embodiments, the length can not exceed 10 mm, 20 mm, 25 mm, or 50 mm, and the width can not exceed 10 mm, 20 mm, 25 mm, or 50 mm. Thus, the surface area of the substrate 202 can be less than 100 mm2(i.e., 10 mm x 10 mm), 400 mm2(i.e., 20 mm x 20 mm), 625 mm2(i.e., 25 mm x 25 mm), or 2,500 mm2(i.e., 50 mm x 50 mm). In other embodiments, the length and / or width can exceed 50 mm, and thus the surface area of the substrate 202 can exceed 625 mm2, as there are no substantial size limitations on the electromechanical actuator 200.

[0029] The stator assembly 232 and the plunger assembly 234 can be connected to each other by one or more flexures, and these flexures are intended to constrain lateral motion of the plunger assembly 234 when it moves vertically within the stator assembly 232 cavity, as well as to control, suppress, or limit tilting. Specifically, the flexures can be designed to provide a desired axial force when the plunger assembly 234 is latched, such that the axial force provided by the flexures counteracts the latching force, enabling faster motion of the plunger assembly 234 when current is applied to the coils of the stator assembly 232. In some embodiments, multiple flexures are used to constrain both the twisting motion ("tilting") and the horizontal motion of the plunger assembly 234, while in other embodiments a single flexure is used to constrain the horizontal motion of the plunger assembly 234 with generally less constraint on twisting.

[0030] The flexures 208, 222 are flexible mechanisms that require a relatively small force to actuate in the actuation direction (i.e., to deflect along the central longitudinal axis 238, but a much larger force to deflect in any other direction. As discussed further below, the flexures 208, 222 can represent different portions of the same flexure that flexibly connects the stator assembly 232 and the plunger assembly 234. This property largely constrains the plunger assembly 234 to take the same path through the center of the stator assembly 232 each time it is actuated. In addition, this property largely or completely eliminates friction between the stator assembly 232 and the plunger assembly 234 and limits rotation of the plunger assembly 234 within the cavity 236 of the stator assembly 232. In Figure 2A In the illustrated embodiment, the flexures 208, 222 (again, which can represent different components of a single flexure) can exert a "biasing force" on the plunger assembly 234 in either direction, which allows for a higher initial actuation force (and thus faster displacement) during actuation. Typically, the flexures 208, 222 are composed of a metal, metal alloy, or polymer.

[0031] As Figure 2A illustrated, the stator assembly can include a series of ferromagnetic layers with a coil disposed therebetween. During actuation, an electrical current is applied to the coil to magnetically polarize the series of ferromagnetic layers, as discussed further below. In Figure 2A In the illustrated embodiment, the stator assembly 232 includes three ferromagnetic layers in a group, namely a first ferromagnetic layer 210 (also referred to as a "bottom ferromagnetic layer"), a second ferromagnetic layer 214 (also referred to as a "middle ferromagnetic layer"), and a third ferromagnetic layer 216 (also referred to as a "top ferromagnetic layer"). Typically, the bottom and middle ferromagnetic layers 210, 214 extend circumferentially around the cavity 236, and thus can have an annular form. Meanwhile, the top ferromagnetic layer 216 can span the entire width of the stator assembly 232, such that its bottom surface defines the upper end of the cavity 236. Although Figure 2A The top ferromagnetic layer 216 is illustrated as having a disc-like shape, but the top ferromagnetic layer 216 can have an annular form similar to the middle and bottom ferromagnetic layers 214, 210. In such embodiments, a hole in the top ferromagnetic layer 216 can allow for viewing and / or gauging the motion of the plunger assembly 234, and / or connecting additional loads at the top of the plunger. Note that the hole can be sized to ensure that its diameter is smaller than the diameter of the top ferromagnetic plate 230 to ensure that the plunger assembly 234 is fully constrained within the cavity of the stator assembly 232.

[0032] The bottom, middle, and top ferromagnetic layers 210, 214, 216 are typically only thick enough to prevent magnetic saturation of the plunger assembly 234 as it is actuated within the cavity 236 of the stator assembly 232. Typically, the thickness of the bottom, middle, and top ferromagnetic layers 210, 214, 216 is no more than 0.4 millimeters (preferably 0.3 millimeters). Most other layers included in the stator assembly 232 are less constraining, and thus can be determined according to the intended application of the electromechanical device 200. For example, the thickness of the "coil stack" can depend on the number of coils, while the thickness of the spacer 206 can depend on the plunger assembly 234, as the bottom of the plunger assembly 234 must be able to move in the cavity 236 between the top surface of the load stops 204A-204B and the bottom surface of the bottom ferromagnetic layer 210. The load stops 204A-204B are the surfaces that the load 218 contacts at the "closed" end of its travel. The load stops 204A-204B can have different uses depending on the device into which the actuator is incorporated. For example, in a relay, the load stops 204A-204B can be conductive elements that are shorted together by the load 218 when the load 218 is in the closed position. In a MEMS valve, the load stops 204A-204B (or a single load stop) can be a valve seat. In this case, the load 218 would be the valve itself, and would seal against the valve seat in the closed position. Thus, the load stops 204A-204B are not necessarily "stops" in the sense of limiting the travel of the load 218, but are rather surfaces that the load 218 contacts at the "closed" end of its travel. Figure 2A The surfaces that the plunger contacts are shown in FIG. 3 to illustrate plunger contact. Note that various intermediate layers (e.g., flexures and spacers) are not shown for simplicity Figure 2A The thickness of all layers shown is 25 μm - 375 μm, and the width is 1.5 mm - 6 mm, although the dimensions can depend on the intended application of the electromechanical actuator (200). Figure 2A The thickness of all layers shown is 25 μm - 375 μm, and the width is 1.5 mm - 6 mm, although the dimensions can depend on the intended application of the electromechanical actuator (200).

[0033] One or more coils can be disposed between each set of ferromagnetic layers. For example, in Figure 2AIn the illustrated embodiment, the first plurality of coils is disposed between the bottom ferromagnetic layer and the middle ferromagnetic layer 210, 214, and the second plurality of coils is disposed between the middle ferromagnetic layer and the top ferromagnetic layer 214, 216. Such a design results in the bottom ferromagnetic layer 210 being proximate to the load block 204A-204B, the first plurality of coils being proximate to the bottom ferromagnetic layer 210, the middle ferromagnetic layer 214 being proximate to the first plurality of coils, the second plurality of coils being proximate to the middle ferromagnetic layer 214, and the top ferromagnetic layer 216 being proximate to the second plurality of coils. Note that the term "proximate" as used herein can refer broadly to a spatial relationship between two components. A first component can be "proximate" to a second component without their respective sides necessarily abutting one another. Thus, there can be one or more intervening components between components that are "proximate" to one another. In contrast, the term "directly proximate" generally refers to components that abut one another and are free of any intervening components therebetween, except for adhesives or other materials necessary to bond them.

[0034] In Figure 2A In the illustrated embodiment, the first plurality of coils includes a pair of coils 212A-212B, and the second plurality of coils also includes a pair of coils 212C-212D. Although in Figure 2A While in the illustrated embodiment the first plurality of coils and the second plurality of coils contain the same number of coils, the first plurality of coils and the second plurality of coils can contain different numbers of coils. For example, a single coil can be disposed between a pair of ferromagnetic layers. The number of coils required can depend on the force required to actuate at a given latching force, the drive voltage and current required, and the acceleration required to meet a desired opening time requirement and / or closing time requirement.

[0035] In operation, current is applied to the coils 212A-212D, as discussed further below. At this time, the coils 212A-212D generate magnetic fields that are in opposite directions, such that the bottom, middle, and top ferromagnetic layers 210, 214, 216 in the stator assembly 232 have a north-south-north ("N-S-N") configuration or a south-north-south ("S-N-S") configuration from top to bottom, depending on the direction of the current. Note that the term "inner pole" is used to describe the radial end of each ferromagnetic layer that is closest to the plunger assembly 234. Because the plunger assembly 234 has two fixed poles (i.e., a north-south configuration or a south-north configuration, defined by the orientation of the permanent magnets 228 at the time of manufacture of the plunger assembly 234), all adjacent poles between the stator assembly 232 and the plunger assembly 234 will push or pull in the same direction, and reversing the direction of the current will reverse the direction in which the stator assembly 232 and the plunger assembly 234 are pushed or pulled.

[0036] The plunger assembly 234 represents another set of layers disposed in the cavity 236 of the stator assembly 232 and that move along a central longitudinal axis 238 between a first position and a second position in operation.

[0037] As mentioned above, the stator assembly 232 and the plunger assembly 234 can be connected to each other by one or more flexure members. In Figure 2A In the illustrated embodiment, features 208 and 222 represent different regions of a single flexure member layer. Thus, the inner flexure member region 222 can be directly connected to the outer flexure member region 208, although the inner flexure member region 222 can move vertically with the plunger assembly 234 by elastic deformation of the flexure member layer, the outer flexure member region 208 can remain stationary (embedded in the layer of the stator assembly 232) despite being connected to the inner flexure member region 222. The flexure member can be designed to allow vertical displacements of 0 microns to 25 microns, 25 microns to 100 microns, 100 microns to 150 microns, 150 microns to 200 microns, 200 microns to 250 microns, or greater than 250 microns. The flexure member can have various forms. For example, the flexure member can have a disc shape with a circular ring, or the flexure member can have a central circular portion and a hexagonal ring connected by three flexure interconnection segments (also referred to as "arms"). In Figure 2A In the illustrated embodiment, the outer flexure member region 208 is a hexagonal ring, and the inner flexure member region 222 is a central circular portion. Thus, the outer and inner flexure member regions 208 and 222 are part of the same layer. In embodiments in which the electromechanical device 200 includes multiple flexure members, the flexure members can be arranged at different heights along a "stack." Having multiple flexure members can provide better (i.e., more robust) angular control of the motion of the plunger assembly 234, preventing the plunger assembly 234 from "tilting" when moving vertically. Additional flexure members can also allow stress to be distributed among them, resulting in longer fatigue life and / or additional material options.

[0038] A spacer 224 can be disposed along the top surface of the flexure member 222 such that, when the plunger assembly 234 is in a first position, the bottom of the spacer 224 is horizontally aligned with the bottom ferromagnetic layer 210 of the stator assembly 232, as illustrated in Figure 2A When the plunger assembly 234 is in a second position, the top of the spacer 224 can be horizontally aligned with the bottom ferromagnetic layer 210 of the stator assembly 232. At a high level, the thickness of the spacer 224 can be selected to accommodate the controlled motion of the plunger assembly 234.

[0039] A plunger element (or simply "plunger") can be disposed along the top surface of the spacer 224. The plunger element can include a permanent magnet 228 with a top and bottom magnetic pole bonded, laminated, or otherwise fixed with ferromagnetic plates. Specifically, a bottom ferromagnetic plate 226 can be connected along the bottom magnetic pole of the permanent magnet 228, and a top ferromagnetic plate 230 can be connected along the top magnetic pole of the permanent magnet 228. As Figures 2A-2CAs shown, the top and bottom ferromagnetic plates 226, 230 can be located between the ferromagnetic layers in the stator assembly 232. Specifically, the bottom ferromagnetic plate 226 can be located between the bottom and middle ferromagnetic layers 210, 214, while the top ferromagnetic plate 230 can be located between the middle and top ferromagnetic layers 214, 216. In operation, the top and bottom ferromagnetic plates 226, 230 can couple the permanent magnet 228 to the bottom, middle, and top ferromagnetic layers 210, 214, 216 by providing a low reluctance path for the magnetic fields generated by the coils 212A-212D.

[0040] Thus, the plunger assembly 234 can include: (i) a load 218, which is a component driven by the actuator that performs some function when in motion; (ii) a flexure 222 for controlling vertical motion along the central longitudinal axis 238; (iii) a spacer 224; and (iv) a permanent magnet 228 having a top and bottom pole fixed with top and bottom ferromagnetic plates 230, 226. The top ferromagnetic plate 230 can be located between the top and middle ferromagnetic layers 216, 214 of the stator assembly 232, while the bottom ferromagnetic plate 226 can be located between the middle and bottom ferromagnetic layers 214, 210.

[0041] The thickness of the permanent magnet 228 is typically maximized under the constraints of the surrounding layers and the application of the electromechanical actuator 200, whether mechanical or magnetic. For example, the magnet thickness can be selected to not exceed the saturation flux density of the ferromagnetic plates 26, 230. Similarly, the magnet thickness can also be selected such that the total magnetic flux is sufficient to produce sufficient latching force to accommodate the intended application of the particular embodiment. Mechanical constraints on the magnet thickness can include that the vertical distance between the top surface of the top ferromagnetic plate 226 and the bottom surface of the bottom ferromagnetic plate 230 does not exceed the difference between the thickness of the middle ferromagnetic layer 214 and the intended stroke length. The thickness of the permanent magnet 228 can typically be set such that at the top end of the stroke, the top ferromagnetic plate 230 contacts the top ferromagnetic layer 216 at the same time as the bottom ferromagnetic plate 226 contacts the middle ferromagnetic layer 214, and at the bottom end of the stroke, the top ferromagnetic plate 230 contacts the middle ferromagnetic layer 214 at the same time as the bottom ferromagnetic plate 226 contacts the bottom ferromagnetic layer 210 (i.e., equal gap on both sides). This tends to maximize the magnetic force (whether latching or actuation) by minimizing the gap in the magnetic circuit at either end of the stroke.

[0042] Similar to stator assembly 232, the dimensions of the layers in plunger assembly 234 are generally unconstrained and can therefore be determined based on the intended application of electromechanical actuator 200. However, permanent magnet 228, bottom ferromagnetic plate 226, and top ferromagnetic plate 230 can be designed with stator assembly 232 in mind. For example, permanent magnet 228, bottom ferromagnetic plate 226, and top ferromagnetic plate 230 should be designed such that: (i) top ferromagnetic plate 230 is movable within the gap between the top surface of intermediate ferromagnetic layer 214 and the bottom surface of top ferromagnetic layer 216, and (ii) bottom ferromagnetic plate 226 is movable within the gap between the top surface of bottom ferromagnetic layer 210 and the bottom surface of intermediate ferromagnetic layer 214.

[0043] like Figure 2A As shown, chamber 236 may not be purely cylindrical. Instead, the layers of stator assembly 232 and / or plunger assembly 234 can be sized and arranged such that chamber 236 has structural features along its longitudinal side, thereby allowing for improved control of plunger assembly 234. For example, consider... Overview of operating principles The embodiment shown. In this embodiment, the top ferromagnetic layer 216 spans the entire periphery of the stator assembly 232. Meanwhile, the intermediate and bottom ferromagnetic layers 214, 210 have the form of annular cylinders (also referred to as "coaxial cylinders"), wherein a central hole corresponds to a cavity 236. These annular cylinders are defined by an inner radius extending from the central longitudinal axis 238 to the inner periphery and an outer radius extending from the central longitudinal axis 238 to the outer periphery. Similarly, each "coil stack" can be in the form of annular cylinders. However, the inner radius of the "coil stack" may differ from the inner radius of the intermediate and bottom ferromagnetic layers 214, 210. When the inner radius of the "coil stack" is larger than the inner radius of the intermediate and bottom ferromagnetic layers 214, 210, structural features (commonly referred to as "notches" or "boobs") are formed that accommodate the top and bottom ferromagnetic plates 230, 226, as discussed above.

[0044] Figure 3

[0045] As mentioned above, the electromechanical actuator 200 can be driven by applying a fixed current pulse through coils 212A-212D.

[0046] To move the plunger assembly 234 from the first position to the second position, current is applied to the coils 212A-212D such that current flows in a first direction. As the plunger assembly 234 moves from the first position to the second position, downward movement can be impeded by any of: (i) mechanical resistance of the flexures 208, 222, (ii) the top ferromagnetic plate 230 contacting the top surface of the middle ferromagnetic layer 214, (iii) the bottom ferromagnetic plate 226 contacting the top surface of the bottom ferromagnetic layer 210, or (iv) the load 218 contacting a component at one end of its travel.

[0047] To move the plunger assembly 234 from the second position to the first position, current is applied to the coils 212A-212D such that current flows in a second direction opposite the first direction. As the plunger assembly 234 moves from the second position to the first position, upward movement can be impeded by any of: (i) mechanical resistance of the outer and inner flexure regions 208, 222, (ii) the top ferromagnetic plate 230 contacting the bottom surface of the top ferromagnetic layer 216, or (iii) the bottom ferromagnetic plate 226 contacting the bottom surface of the middle ferromagnetic layer 214. Thus, upward movement can be impeded by the flexures reaching a stretch limit at which their restoring force prevents further axial movement, or upward movement can be impeded by the top ferromagnetic layer 230 or the middle ferromagnetic layer acting as a physical barrier.

[0048] Thus, to actuate the plunger assembly 234, a fixed current pulse obtained from a power source (not shown) can be applied to the coils 212A-212D of the stator assembly 232, as this operation causes the top, middle, and bottom ferromagnetic layers 216, 214, 210 to be magnetically polarized. Positive current can cause the plunger assembly 234 to move to the first position, thereby moving the load 218 to the "open" position. Conversely, negative current can cause the actuator assembly 234 to move to the second position, thereby moving the load 218 to the "closed" position. Figure 3 A simplified schematic diagram including the electromechanical actuator latching behavior caused by the magnetic circuits of the "open position" and the "closed position." In Figure 3 the dotted lines represent magnetic flux in one magnetic circuit, and the dash-dot lines represent magnetic flux in the other magnetic circuit. Magnetic flux in one direction (represented by the dotted lines) causes the electromechanical actuator to "open," while magnetic flux in the opposite direction (represented by the dash-dot lines) causes the electromechanical actuator to "close." Note that in A. Magnetic latching a portion of the plunger assembly is shown.

[0049] Note that while the load 218 can be described as being in an "open" position or a "closed" position, one skilled in the art will recognize that these positions can simply be relative end positions. Thus, the "open" position can also be referred to as the "first end position" or simply the "first position," and the "closed" position can also be referred to as the "second end position" or simply the "second position."

[0050] Figure 2A

[0051] One important aspect of an electromechanical actuator is its actuation method. Conventional electromechanical actuators can require continuous application of current to maintain a given state (e.g. closed state). To avoid the need for continuous application of current for the electromechanical actuator to remain open or closed, the electromechanical actuator can be designed to "latch" in position at state switching. This is achieved by designing the actuator to be magnetically bistable.

[0052] Reference is made to B. Magnetic actuation The spacing between the top, middle, and bottom ferromagnetic layers 216, 214, 210 in the stator assembly 232 can be matched to the spacing of the top and bottom ferromagnetic plates 230, 226 (and permanent magnets 228 and spacers 224) of the plunger assembly 234. When the plunger is in its highest and lowest positions, the distance that the magnetic field lines generated by the coils 212A-212D travel through non-ferromagnetic material is minimized, which is maximized when the spacing is matched. This creates two local minima in magnetic reluctance (and thus potential energy) at these positions, resulting in the plunger "latching" to its highest and lowest positions, with the magnetic "latching force" being maximized when the spacing is matched.

[0053] The size of the permanent magnets 228, the thickness of the top and bottom ferromagnetic plates 230, 226, the vertical spring constants of the outer and inner flexure regions 208, 222, and the distance between the highest and lowest positions all contribute to the latching force. To maximize actuation speed, the net latching force (including both magnetic and flexure contributions) can be minimized within the constraints of the vibration and shock resistance settings. Because the actuation force (which should be maximized to optimize switching speed) is determined primarily by the sum of the magnetic latching force and the vertical flexure force, the geometry of the flexure is often the most easily manipulated parameter. Thus, the flexure spring constant is selected to set the "net latching force" at an appropriate value, which is often more desirable than redesigning or reselecting the permanent magnets 228 or the top and bottom ferromagnetic plates 230, 226, or using a larger distance (also referred to as "gap size").

[0054] Figure 4

[0055] Figure 3 An illustration is included showing that the application of current through the coils 406A-N, 410A-N will result in a constant magnetic force being applied to the plunger 402. To better show the magnetic forces, the electromechanical actuator 400 has been "unwrapped" such that the layers are separated and "expanded", and thus the layers are not drawn to scale.

[0056] As discussed above, the stator assembly 420 can include three sets of ferromagnetic layers with coils disposed therebetween such that (i) at least one coil is disposed between the bottom ferromagnetic layer and the middle ferromagnetic layer 404, 408 and (ii) at least one coil is disposed between the middle ferromagnetic layer and the top ferromagnetic layer 408, 412. For example, a first plurality of coils 406A-N can be disposed between the bottom ferromagnetic layer and the middle ferromagnetic layer 404, 408 and a second plurality of coils 410A-N can be disposed between the middle ferromagnetic layer and the top ferromagnetic layer 408, 412. The first plurality of coils and the second plurality of coils 406A-N, 410A-N can contain the same number of coils or the first plurality of coils and the second plurality of coils 406A-N, 410A-N can contain different numbers of coils. Generally, each plurality of coils 406A-N, 410A-N includes at least two coils, although any number of coils can be disposed between the bottom and middle ferromagnetic layers 404, 408 or between the middle ferromagnetic layer and the top ferromagnetic layer 408, 412. The thickness of each "coil stack" can depend on the dimensions of the plunger 402, for example. The thickness of each "coil stack" tends to be directly proportional to the number of coils it contains.

[0057] Similar to Figure 4 , Figure 4 Only the plunger 402 of the actuator assembly is shown in FIG. 4. The plunger 402 can include a permanent magnet 414 with a top magnetic pole and a bottom magnetic pole to which ferromagnetic plates 416, 418 are affixed. Here, for example, the bottom ferromagnetic plate 416 is attached along the bottom magnetic pole (i.e., the south pole) of the permanent magnet 414 and the top ferromagnetic plate 418 is attached along the top magnetic pole (i.e., the north pole) of the permanent magnet 414.

[0058] The top, middle, and bottom ferromagnetic layers 412, 408, 404 can be interleaved with the top and bottom ferromagnetic plates 416, 418 as shown in Figure 4 The top ferromagnetic plate 418 can be located between the top and middle ferromagnetic layers 412, 408 and the bottom ferromagnetic plate 416 can be located between the middle and bottom ferromagnetic layers 408, 404.

[0059] As mentioned above, the application of current through the coils 406A-N, 410A-N results in the application of a constant magnetic force to the plunger 402 (more specifically, to the top and bottom ferromagnetic plates 418, 416). This constant magnetic force is generally directly proportional to the current and the number of turns of the coils 406A-N, 410A-N. When this constant magnetic force overcomes the "latching force" of the plunger 402 (more specifically, the permanent magnet 414), the plunger 402 will begin to move downward (e.g., toward the bottom ferromagnetic layer 404) or upward (e.g., toward the top ferromagnetic layer 412).

[0060] Applying a positive current to coils 406A-N and 410A-N can achieve movement in one direction (e.g., upward). Applying a negative current to coils 406A-N and 410A-N may result in movement in the other direction (e.g., downward). For example, a positive current may cause plunger 402 to move upward until the top ferromagnetic plate 418 contacts the bottom surface of the top ferromagnetic layer 412 and / or the bottom ferromagnetic plate 416 contacts the bottom surface of the intermediate ferromagnetic layer 408. When plunger 402 is in this position, electromechanical actuator 400 can be described as "on". Conversely, a negative current may cause plunger 402 to move downward until the top ferromagnetic plate 418 contacts the top surface of the intermediate ferromagnetic layer 408 and / or the bottom ferromagnetic plate 416 contacts the top surface of the bottom ferromagnetic layer 404. When plunger 402 is in this position, electromechanical actuator 400 can be described as "off".

[0061] Various parameters affect this constant magnetic force and the speed at which the plunger 402 moves between positions. These parameters include: ● Thickness and composition of the top ferromagnetic layer, middle ferromagnetic layer and bottom ferromagnetic layer 412, 408 and 404.

[0062] For example, the thickness of the top ferromagnetic layer, the middle ferromagnetic layer, and the bottom ferromagnetic layer can be 25 μm - 325 μm.

[0063] ● Thickness and grade of permanent magnet 414.

[0064] For example, the thickness of the permanent magnet 414 can be 0.2 mm - 0.5 mm.

[0065] ● Number of turns for coils 406A-N and 410A-N.

[0066] ● The magnitude of the current applied to coils 406A-N and 410A-N.

[0067] ● Diameter of coils 406A-N, 410A-N and permanent magnet 414.

[0068] ● The spacing and overlap between the top ferromagnetic layer, the middle ferromagnetic layer and the bottom ferromagnetic layer 412, 408 and 404 affect the direction of the magnetic field gradient due to spatial relationships.

[0069] In operation, current is applied to the coils 406A-N, 410A-N. At this point, the coils 406A-N, 410A-N generate magnetic fields in opposite directions to induce magnetic poles in the top, middle, and bottom ferromagnetic layers 412, 408, 404. Depending on the current direction, the inner magnetic poles of the top, middle, and bottom ferromagnetic layers 412, 408, 404 can be in an N-S-N configuration or an S-N-S configuration. The permanent magnet 414 has two fixed magnetic poles. Here, for example, the permanent magnet has an N-S configuration. Thus, when the top, middle, and bottom ferromagnetic layers 412, 408, 404 are magnetically polarized, all of the inner magnetic poles of the stator assembly 420 will push or pull the plunger 402 in the same direction. Reversing the current direction will reverse the direction in which the inner magnetic poles of the stator assembly 420 push or pull the plunger 402. Figures 5A-5E It is shown how applying current to the coils 406A-N, 410A-N can induce magnetic polarization, thereby exerting a magnetic force on the plunger 402.

[0070] Figure 5A A visualization is included showing the magnetic field strength and direction as the plunger assembly moves between the first position and the second position. Specifically, Figure 5B The plunger assembly is shown in the first position. To move the plunger assembly to the second position, a fixed positive current pulse can be applied to the coils to magnetically attract the plunger assembly downward. Figure 5C The plunger assembly is shown moving to the second position, while Figure 5D The plunger assembly is shown in the second position. To move the plunger assembly back to the first position, a fixed negative current pulse can be applied to the coils to magnetically attract the plunger assembly upward. Figure 5E The plunger assembly is shown moving to the first position, while C. Constrained motion and flexure The plunger assembly is shown returning to the first position.

[0071] Figure 2A

[0072] The flexures (e.g. Figure 2A The flexures 208, 222 of the plunger assembly 200 can be used to keep the plunger assembly centered in the stator assembly cavity, ensuring that the motion is primarily, if not exclusively, vertical motion along the central longitudinal axis. Furthermore, these flexures can dampen or prevent friction between the plunger assembly and the stator assembly layers. To this end, the flexures can need to have a stiffness with respect to lateral motion that is at least the maximum lateral magnetic force (worst-case assumptions on geometry within manufacturing tolerances) divided by the worst-case gap within manufacturing tolerances.

[0073] To ensure that the load (e.g. Figure 2A The load 218 of the plunger assembly 200 can be designed to be flat, and the load stop 224 of the stator assembly 400 can be designed to be flat. To this end, the load 218 can need to have a stiffness with respect to lateral motion that is at least the maximum lateral magnetic force (worst-case assumptions on geometry within manufacturing tolerances) divided by the worst-case gap within manufacturing tolerances. Figure 6The maximum lateral asymmetry of the flexure force can be less than the remaining closure side latching force after accounting for any force exerted by the flexure on the top surface of the load stop 204A-204B.

[0074] Figure 6 including a perspective cross-sectional view showing how the flexure 602 connected to the plunger assembly 604 constrains the motion of the plunger assembly 604 relative to the stator assembly 606. To ensure the flexure 602 is positioned correctly, the flexure 602 can be "sandwiched" between layers of the plunger assembly 604 and / or the stator assembly 606. For example, the flexure 602 can be inserted between ceramic layers.

[0075] For simplicity, Figure 6 only some components of the plunger assembly and stator assembly 604, 606 are shown in the middle. Specifically, Figure 6 shows how the flexure 602 ensures that the motion of the load 608 is substantially vertical or longitudinal, i.e., along the longitudinal axis 610. While some degree of tilt can occur, the plunger assembly 604 does not experience any significant horizontal or lateral motion, nor does it experience any significant rotation about the longitudinal axis.

[0076] As Packaging and internal environment shown, this method of guiding the motion of the plunger assembly 604 not only allows for highly consistent and repeatable motion, but also avoids any friction of the plunger assembly 604 contacting the inner walls of the stator assembly 606. Such friction can lead to poor and / or unreliable performance, so it is important to avoid such friction.

[0077] Design choices

[0078] Embodiments of the electromechanical actuator can benefit from hermetic sealing to prevent fluids (e.g., gases and liquids) from entering the chamber of the stator assembly from the ambient environment, or from the ambient environment into the chamber of the stator assembly.

[0079] In addition to hermetic sealing, embodiments of the electromechanical actuator can be evacuated or have an insulating fluid deposited or injected therein. For example, the chamber defined within the stator assembly can be filled with a chemically inert, electrically insulating gas at a pressure higher or lower than one atmosphere, or the chamber can be filled with a chemically inert, electrically insulating liquid at a pressure higher or lower than one atmosphere. If used in an electromechanical relay, the chamber can be filled with an insulating fluid to provide sufficient dielectric resistance for a given stroke length of the plunger assembly. Atmospheric pressures in excess of one atmosphere will also result in a pressure bias applied across any leak paths through the hermetic enclosure, thereby inhibiting or preventing atmospheric ingress into the chamber. The liquid in the chamber can be electrically insulating or conductive depending on the application. The liquid can serve as a means to transfer hydraulic pressure, or provide dielectric breakdown resistance.

[0080] Typically, the insulating fluid is a chemically inert, electrically insulating gas that consists entirely or predominantly of nitrogen. However, the nitrogen can be mixed with one or more other electrically insulating gases, for example, to improve arc resistance (as can be useful for electromechanical relays). However, other fluids can be used. For example, the insulating fluid can be another chemically inert, electrically insulating gas, such as argon, or the insulating fluid can be a chemically inert, electrically insulating liquid, such as hexamethyldisiloxane or octamethyltrisiloxane, which are low-molecular-weight, low-viscosity silicone oils.

[0081] Design and manufacturing methods for electromechanical actuators

[0082] Because the actuation force is proportional to the acceleration, the total initial force at the start of the "stroke" disproportionately determines the time required to switch from one state to another. Note that the total initial force can be broadly characterized as the sum of the latching force, the actuation force, and the flexure force. To maximize the force at the start of the "stroke," the flexure can act as a spring to counteract the latching force. When the latching force is partially, if not completely, counteracted, the total initial force can be characterized as the sum of the actuation force and the flexure force.

[0083] Figure 7

[0084] To design an electromechanical actuator according to the embodiments disclosed herein, it is easiest to view the electromechanical actuator as a combination of two assemblies, namely (i) a stator assembly having a chamber partially defined along a central longitudinal axis through the stator assembly, and (ii) a plunger assembly disposed in the chamber of the stator assembly and in operation moved along the central longitudinal axis between a first position and a second position. At a high level, the stator assembly comprises two sub-assemblies, namely (i) a contact assembly and (ii) a drive electromagnetic assembly. Figure 8 A schematic of the plunger assembly 702 including the stator assembly 704 and the stator assembly 708. As discussed above, the stator assembly 708 facilitates actuation of the plunger assembly 702 by generating a magnetic field when current is applied. Actuation of the plunger assembly 702 causes its bottommost surface to engage or disengage the load stop 706.

[0085] Manufacture of the electromechanical actuator requires separate manufacture of its sub-assemblies. Figure 2A A schematic including a set of steps that can be used to assemble the relay 200 as a set of layers. Note that for convenience, reference can be made to the components discussed above. Figure 8 The order of assembly is important because the flexure layers (represented by the flexure regions 208, 222 belonging to the same flexure) are contained in both sub-assemblies. Moreover, the interlocking aspect of the ferromagnetic layers requires that the plunger assembly must be assembled in situ because it cannot be inserted through the opening of the intermediate ferromagnetic layer 214 after the plunger assembly 234 is assembled. For illustrative purposes, Figure 9 One possible assembly sequence is shown below: Step 1 : Start with spacer 1 rigidly connected between plunger assembly 234 and stator assembly 232 by removable label marked "x".

[0086] Step 2: Load 2 laminated onto spacer 1.

[0087] Step 3: Bottom ferromagnetic layer 210 laminated onto the assembly produced in Step 2.

[0088] Step 4: Spacers 224, bottom ferromagnetic plate (226), and magnets 228 of plunger assembly 234 laminated into the opening left inside bottom ferromagnetic layer 210.

[0089] Step 5: First set of coils 212A-212B and middle ferromagnetic layer 214 laminated onto the assembly produced in Step 4.

[0090] Step 6: Top ferromagnetic plate 230 laminated onto the top of magnets 228.

[0091] Step 7: Second set of coils 212C-212D and top ferromagnetic layer 216 laminated onto the top of the assembly produced in Step 6.

[0092] Step 8: Spacer layer 206 laminated onto the bottom of the assembly produced in Step 7. Then, the label (x) applied in Step 1 is removed to free the motion of plunger assembly 234, which is constrained by flexures (collectively denoted as 208 and 222).

[0093] Step 9: Place the assembly produced in Step 8 over load stops 204A-204B. Load stops 204A-204B can be laminated or clamped into place under the assembly.

[0094] One skilled in the art will recognize that other assembly sequences are possible and, in some embodiments, can be desirable based on the speed or precision with which the electromechanical actuator 200 is assembled.

[0095] Figure 2A A high-level diagram of a process 900 for manufacturing an electromechanical actuator is included. Again, for convenience, reference can be made to the components discussed Figure 9 above. However, Figure 2A particular to electromechanical actuator designs that do not include flexures connecting the stator assembly and the plunger assembly.

[0096] Initially, a manufacturer can manufacture a top ferromagnetic layer (step 901), for example, by cutting a single layer from a piece of ferromagnetic material (e.g., steel). Then, the manufacturer can manufacture a plunger (step 902). For example, the manufacturer can create or obtain a permanent magnet, and then laminate ferromagnetic plates along its top and bottom magnetic poles. These ferromagnetic plates can be referred to as "top ferromagnetic plates" and "bottom ferromagnetic plates," respectively. Thereafter, the manufacturer can manufacture a plunger assembly by laminating, gluing, or otherwise connecting spacers and loads to the bottom ferromagnetic plates (step 903). Note that additional layers can be included in the plunger assembly.

[0097] To manufacture a stator assembly, a manufacturer can obtain a substrate (step 904), glue components that interact with the load to a top surface of the substrate (step 905), and then laminate ferromagnetic layers and coil layers to the top surface of the pair of contacts in an alternating fashion (step 906). Typically, the ferromagnetic layers and coils are laminated such that the resulting electromechanical actuator includes three ferromagnetic layers in a group, one or more coils disposed between a first ferromagnetic layer and a second ferromagnetic layer, and another one or more coils disposed between the second ferromagnetic layer and a third ferromagnetic layer. In some embodiments, the lowermost ferromagnetic layer is laminated directly adjacent to the pair of contacts, while in other embodiments, one or more intermediate layers are present, such as Notes

[0098] To create an electromechanical actuator, a manufacturer can dispose the plunger assembly within a cavity defined by the stator assembly, and then glue the top ferromagnetic layer to the stator assembly (step 907). Gluing the top ferromagnetic layer to the stator assembly results in a fully enclosed cavity inside the stator assembly. As described above, in operation, the plunger assembly is capable of moving between different positions within the fully enclosed cavity.

[0099] ​

[0100] The preceding description of various embodiments of the claimed subject matter is provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the claimed subject matter to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the claimed subject matter be limited only by the claims and equivalents thereof. The embodiments were chosen and described in order to best explain the principles of the application and its practical application to thereby enable others skilled in the art to best utilize the claimed subject matter, various embodiments, and various modifications as are suited to the particular use contemplated.

[0101] ​While the detailed description describes certain embodiments and the best mode contemplated, the technology can be practiced in a variety of ways, despite the detailed description looking somewhat different. Embodiments can vary widely in their implementation details, while still being encompassed by the specification. The particular terminology used in the description of various embodiments should not be taken as limiting the technology to the specific features, features, or aspects with which the terminology is associated. In general, the terminology used throughout has been chosen for readability and instructional purposes. It is the intent of the inventor / owner to include all changes, alterations and modifications under the scope and spirit of the key claims after the patent grant. Therefore, the actual scope of the technology is not limited to the disclosed embodiments but encompasses all equivalent ways of practicing or realizing the technology.

[0102] The language used in the specification is intended to be read in light of the patent statutes. It can not be chosen as to be used for limiting or defining the subject matter. Therefore, the scope of the technology should not be limited by this detailed description but by any claims that issue based on this application. The disclosure of various embodiments is intended to be illustrative, and not to limit the scope of the technology as set forth in the following claims.

[0103] This application claims priority to U.S. Application No. 63 / 497,361, filed April 20, 2023, which is incorporated by reference in its entirety.

Claims

1. An electromechanical actuator, comprising: A stator assembly having a cavity that is partially defined through the stator assembly along a central longitudinal axis. The stator assembly includes: A non-conductive substrate having a top surface. One or more layers, including components to which the load interacts mechanically or electrically. First ferromagnetic layer, adjacent spacer The first plurality of coils are located adjacent to the first ferromagnetic layer. The second ferromagnetic layer is adjacent to the first plurality of coils. The second plurality of coils, adjacent to the second ferromagnetic layer, and A third ferromagnetic layer, adjacent to the second plurality of coils, wherein the bottom surface of the third ferromagnetic layer defines the top of the chamber; and A plunger assembly disposed within the chamber of the stator assembly and moving during operation between a first position and a second position along the central longitudinal axis. The plunger assembly includes: A plunger, comprising a pair of ferromagnetic plates and a magnet disposed between the pair of ferromagnetic plates, Wherein, (i) the first ferromagnetic plate of the pair of ferromagnetic plates is disposed between the first ferromagnetic layer and the second ferromagnetic layer, and (ii) the second ferromagnetic plate of the pair of ferromagnetic plates is disposed between the second ferromagnetic layer and the third ferromagnetic layer.

2. The electromechanical actuator according to claim 1, wherein, When the plunger assembly is in the first position, the opening below the plunger assembly is naturally filled with insulating gas.

3. The electromechanical actuator according to claim 1, wherein, To move the plunger assembly from the first position to the second position, current is applied to the first plurality of coils and the second plurality of coils, such that the current flows in a first direction.

4. The electromechanical actuator according to claim 1, wherein, When the plunger assembly moves from the first position to the second position, the movement is hindered by the following: (i) The first ferromagnetic plate contacts the top surface of the first ferromagnetic layer, or (ii) The second ferromagnetic plate contacts the top surface of the second ferromagnetic layer.

5. The electromechanical actuator according to claim 4, wherein, To move the plunger assembly from the second position to the first position, current is applied to the first plurality of coils and the second plurality of coils such that the current flows in a second direction opposite to the first direction.

6. The electromechanical actuator according to claim 1, wherein, When the plunger assembly moves from the second position to the first position, the movement is blocked by the following: (i) The flexible element reaches its extension limit, causing the restoring force to prevent further axial movement. (ii) The first ferromagnetic plate contacts the bottom surface of the second ferromagnetic layer, or (iii) The second ferromagnetic plate contacts the bottom surface of the third ferromagnetic layer.

7. An electromechanical actuator, comprising: A stator assembly having a cavity that is partially defined through the stator assembly along a central longitudinal axis. The stator assembly includes: A group of three ferromagnetic layers, with a coil disposed between the three ferromagnetic layers, such that (i) at least one coil is disposed between the first and second ferromagnetic layers of the group of three ferromagnetic layers, and (ii) at least one coil is disposed between the second and third ferromagnetic layers of the group of three ferromagnetic layers; and A plunger assembly disposed within the chamber of the stator assembly and moving during operation between a first position and a second position along the central longitudinal axis. The plunger assembly includes: A plunger, the plunger comprising a pair of ferromagnetic plates and a magnet disposed between the pair of ferromagnetic plates; Specifically, to move the plunger assembly from the first position to the second position, a current is applied to the coil, causing the current to flow in a first direction, thereby causing the plunger to move along the central longitudinal axis toward a pair of contacts; and In order to move the plunger assembly from the second position to the first position, a current is applied to the coil, causing the current to flow in a second direction opposite to the first direction, thereby causing the plunger to move away from the pair of contacts along the central longitudinal axis.

8. The electromechanical actuator according to claim 7, wherein, (i) the first ferromagnetic plate of the pair of ferromagnetic plates is disposed between the first ferromagnetic layer and the second ferromagnetic layer, and (ii) the second ferromagnetic plate of the pair of ferromagnetic plates is disposed between the second ferromagnetic layer and the third ferromagnetic layer.

9. The electromechanical actuator according to claim 8, in, When the plunger assembly moves from the first position to the second position, the movement is hindered by the following: (i) The first ferromagnetic plate contacts the top surface of the first ferromagnetic layer, or (ii) The second ferromagnetic plate contacts the top surface of the second ferromagnetic layer, and When the plunger assembly moves from the second position to the first position, the movement is hindered by the following: (i) The first ferromagnetic plate contacts the bottom surface of the second ferromagnetic layer, or (ii) The second ferromagnetic plate contacts the bottom surface of the third ferromagnetic layer.

10. The electromechanical actuator according to claim 7, wherein, The pair of ferromagnetic plates are laminated along the top and bottom magnetic poles of the magnet.

11. The electromechanical actuator according to claim 7, wherein, The first plurality of coils are disposed between the first ferromagnetic layer and the second ferromagnetic layer, and The second plurality of coils are disposed between the second ferromagnetic layer and the third ferromagnetic layer.

12. The electromechanical actuator according to claim 11, wherein, The first plurality of coils have the same number of coils as the second plurality of coils.

13. The electromechanical actuator according to claim 7, wherein, Each of the three ferromagnetic layers in a group has a ring-shaped form to completely surround the cavity.

14. The electromechanical actuator according to claim 7, wherein, The amount of current required to move the plunger assembly is based on (i) the thickness of the three ferromagnetic layers in a set, (ii) the grade and thickness of the magnet, (iii) the number of coil turns, or (iv) the size and thickness of the coil.

15. The electromechanical actuator according to claim 7, wherein, The spacing between the three ferromagnetic layers in a group is complementary to the spacing between the pair of ferromagnetic plates, such that when the plunger assembly is in the first and second positions, the distance the magnetic field travels through the non-ferromagnetic material is minimized, thereby making the first and second positions represent local minimum potential energy locations.

16. The electromechanical actuator according to claim 7, wherein, The chamber is filled with a chemically inert, electrically insulating gas at a pressure higher than one atmosphere.

17. The electromechanical actuator according to claim 7, wherein, The chamber is filled with a chemically inert, electrically insulating gas at a pressure below one atmosphere.

18. The electromechanical actuator according to claim 7, wherein, The chamber is filled with a chemically inert, electrically insulating liquid at a pressure higher than one atmosphere.

19. The electromechanical actuator according to claim 7, wherein, The chamber is filled with a chemically inert, electrically insulating liquid at a pressure below one atmosphere.

20. An electromechanical actuator, comprising: A stator assembly having a cavity that is partially defined through the stator assembly along a central longitudinal axis. The stator assembly includes: A group of three ferromagnetic layers, with a coil disposed between the three ferromagnetic layers, the coil being electrically connected to a power source; and A plunger assembly disposed within the chamber of the stator assembly and moving during operation between a first position and a second position along the central longitudinal axis. The plunger assembly includes: A plunger, the plunger comprising at least one ferromagnetic plate and at least one magnet, and When a current is applied to the coil, the three ferromagnetic layers are magnetically polarized, and thus, depending on the direction of the current, the three ferromagnetic layers have a North-South-North (NSN) configuration or a South-North-South (SNS) configuration. The movement of the plunger assembly is determined by the current configuration of the three ferromagnetic layers in a group.

21. An electromechanical actuator comprising (i) a stator assembly and (ii) a plunger assembly, wherein, The stator assembly and the plunger assembly are arranged in layers such that the actuator can be magnetically latched at each end of its stroke.

22. An electromechanical actuator, comprising: A stator assembly having a cavity that is partially defined through the stator assembly along a central longitudinal axis. The stator assembly includes: A group of three ferromagnetic layers, with a coil disposed between the three ferromagnetic layers, such that (i) at least one coil is disposed between the first and second ferromagnetic layers of the group of three ferromagnetic layers, and (ii) at least one coil is disposed between the second and third ferromagnetic layers of the group of three ferromagnetic layers, and The first part of the flexible element; and A plunger assembly disposed within the chamber of the stator assembly and moving during operation between a first position and a second position along the central longitudinal axis. The plunger assembly includes: A plunger, the plunger including a magnet, and The second part of the flexible member; Wherein, in order to move the plunger assembly between the first position and the second position, a current is applied to the coil; and The second part is configured to move with the plunger assembly, while the first part is configured to remain in a fixed position with the stator assembly, so that the movement of the plunger assembly is constrained by the flexible element.

23. The electromechanical actuator according to claim 22, wherein, The flexible element flexibly connects the stator assembly and the plunger assembly together, such that the plunger assembly takes the same path through the chamber during each actuation between the first position and the second position.

24. The electromechanical actuator according to claim 22, wherein, The flexible element is designed to suspend the plunger assembly in the chamber, thereby largely or completely eliminating friction between the plunger assembly and the stator assembly.

25. The electromechanical actuator according to claim 22, wherein, The flexible element is made of metal, metal alloy or polymer.

26. The electromechanical actuator according to claim 22, wherein, The flexible element is designed to allow vertical displacements of 0 to 25 micrometers, 25 to 100 micrometers, 100 to 150 micrometers, 150 to 200 micrometers, 200 to 250 micrometers, or greater than 250 micrometers.

27. The electromechanical actuator according to claim 22, wherein, The flexible element is disk-shaped, having a circular portion representing the second part and an annular portion representing the first part, wherein the circular portion is connected to the annular portion via a plurality of interconnecting segments configured to be flexible.

28. The electromechanical actuator according to claim 22, wherein, The flexible element is designed to provide the required axial force when the actuator is latched, such that the axial force provided by the flexible element counteracts the latching force, thereby supporting faster rotor movement when current is applied to the coil.

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