Reluctance actuator

Abstract

A reluctance actuator (1) comprising a ferromagnetic armature (2) and a ferromagnetic movable element (3) that together form a magnetic circuit, wherein the movable element (3) occupies a position relative to the ferromagnetic armature (2) that depends on the magnetic flux within the ferromagnetic armature (2) and the movable element (3), and the ferromagnetic armature (2) is divided into at least a first portion (2') and a second portion (2") that are movable relative to each other, and one or more variable air gaps (4,5) are provided between the first portion (2') and the second portion (2"), and at least one piezoelectric actuator (6 ,7) is connected to a first part (2') and a second part (2") of a ferromagnetic armature (2), setting one or more variable air gaps (4,5) between the first part (2') and the second part (2"), the ferromagnetic armature (2) is symmetric with respect to a central actuator axis (8) through a permanent magnet (9) that generates magnetic flux lines, the magnetic flux lines are transmitted through a movable element (3) and through both poles (10,11) of the ferromagnetic armature (2) in opposite directions, the movable element (3) is located between the two poles (10,11), and is a reluctance actuator (1).

Description

Technical Field

[0001] The present invention relates to a reluctance actuator comprising a ferromagnetic armature and a ferromagnetic mover that together form a magnetic circuit, wherein the mover occupies a position relative to the ferromagnetic armature that depends on the magnetic flux in the ferromagnetic armature and in the mover.

Background Art

[0002] "https: / / www.engineeringsolutions.philips.com / looking-expertise / high-precision-engineering / comparative-evaluation-of-lorentz-and-reluctance-actuators / " describes a comparative evaluation of Lorentz actuators and reluctance actuators. It is argued that Lorentz actuators (based on current-carrying windings placed in a magnetic field) are widely used to achieve the highest level of force predictability. However, due to their limited force density, significant heating of the coil and local hot spots occur.

[0003] Reluctance actuators are based on the attractive force exerted by a ferromagnetic armature magnetized by a coil on a ferromagnetic mover, thereby enabling significantly higher force density and steepness. However, the latter actuators suffer from greater parasitic effects, which affect the predictability of their force.

[0004] Such reluctance actuators are further known from "https: / / www.acin.tuwien.ac.at / en / project / hybrid-reluctance-actuators-for-high-precision-motion / ".

[0005] In the reluctance actuators described on this website, permanent magnets and coils are used to generate magnetic flux through a ferromagnetic armature and a movable element. The direction of the coil's magnetic flux is opposite to that of the magnet's magnetic flux in one of the variable gaps between the movable element and the armature. These magnetic fluxes cancel each other out. As a result, the total magnetic flux in one of the variable gaps is weaker than the total magnetic flux in the other variable gap on the opposite side of the movable element. The unbalanced magnetic flux on both sides of the movable element imparts a lateral actuation force to the movable element. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The object of the present invention is to solve the problem of heat dissipation caused by the current that must flow through the coil of a reluctance actuator in order to move the movable element and hold it in a desired position. This problem is an obstacle to reluctance actuators replacing conventional Lorentz actuators, despite their advantages over Lorentz actuators. [Means for solving the problem]

[0007] The paper "Linear step motor based on magnetic force control using composite of magnetorestrictive and piezoelectric materials" by Ueno, T. et al., IEEE Transactions on Magnetics, USA, Vol. 43, No. 1, December 19, 2006, pp. 11-14, XP011152115, discloses a composite material for use in a linear step motor, consisting of a giant magnetostrictive material (terphenol-D) and a multilayer piezoelectric transducer (PZT) actuator. The combination of the magnetic circuit and this composite controls the magnetic force applied to the movable yoke by the voltage of the PZT via mechanical stress.

[0008] The paper "Long-range fast nanopositioner using nonlinearities of hybrid reluctance actuator for energy efficiency" by Ito, S et al., IEEE Transactions on Industrial Electronics, IEEE Service Center, Piscataway, New Jersey, USA, Vol. 66, No. 4, June 7, 2018, pp. 3051-3059, XP011703739, discloses a bend-inducing nanopositioner with a nonlinear hybrid reluctance actuator for a wide range and energy efficiency. The actuator has a nonlinear negative stiffness, which partially cancels out the stiffness of the bend.

[0009] The paper "Integrated electromagnetic actuator with adaptable zero power gravity compensation" by Pechacker, A et al., IEEE Transactions on Industrial Electronics, IEEE Service Center, Piscataway, New Jersey, USA, Vol. 71, No. 5, June 26, 2023, pp. 5055-5062, XP011956916, discloses an integrated electromagnetic actuator with a position-independent zero power gravity compensation mechanism for variable mass. Gravity is actively compensated by a variable reluctance actuator with a seamlessly adjustable electromagnetic permanent magnet. The negative stiffness of the variable reluctance actuator is compensated by applying a Lorentz actuator to stabilize the position of the magnetically levitated mover in two degrees of freedom.

[0010] According to the present invention, a reluctance actuator is proposed to have features as defined in any one of the appended claims.

[0011] In a first embodiment of a reluctance actuator comprising a ferromagnetic armature and a ferromagnetic mover that together form a magnetic circuit, the mover occupies a position relative to the ferromagnetic armature that depends on the magnetic flux within the mover, the ferromagnetic armature is divided into at least a first and a second portion that are movable relative to each other, providing one or more variable air gaps between the first and second portions, and at least one piezoelectric actuator is connected to the first and second portions of the ferromagnetic armature, setting one or more variable air gaps between the first and second portions, the present invention proposes that the ferromagnetic armature is symmetric with respect to a central actuator axis passing through a permanent magnet that generates magnetic flux lines, the magnetic flux lines are transmitted through the mover and through both poles of the ferromagnetic armature in opposite directions, and the mover is located between the two poles. This avoids nonlinearity in the reluctance actuator of the present invention as much as possible.

[0012] By using a piezoelectric actuator as part of a reluctance actuator in the manner described above, instead of a coil, to induce the necessary magnetic flux in a ferromagnetic armature, the reluctance of the actuator can be adjusted, and the movable element can be directed to a desired position. In other words, the operation of the piezoelectric actuator changes its dimensions, which in turn changes the reluctance of the actuator (i.e., its resistance to magnetic flux), resulting in a controllable bidirectional force generated in the soft ferromagnetic movable element of the actuator.

[0013] In a preferred embodiment, the actuator comprises two piezoelectric actuators on either side of the movable element, the piezoelectric actuators being used to control the air gap between the first and second parts of the ferromagnetic armature.

[0014] Preferably, the piezoelectric actuator simultaneously controls the air gap between the first and second parts of the ferromagnetic armature.

[0015] In one embodiment, it is preferable that the second portion of the ferromagnetic armature and the movable element are suspended by a bent portion.

[0016] The accompanying drawings are incorporated herein by reference and form part of this specification, illustrating embodiments of the invention and illustrating the principles of the invention together with the description. The drawings are for illustrative purposes only and should not be construed as limiting the invention. [Brief explanation of the drawing]

[0017] [Figure 1] A schematic representation of the first embodiment of the reluctance actuator according to the present invention is shown below. [Figure 2] A second embodiment of the reluctance actuator according to the present invention is schematically shown. [Modes for carrying out the invention]

[0018] Whenever the same reference number is used in a figure, these numbers refer to the same or similar parts.

[0019] The reluctance actuator 1 shown in the figure comprises a ferromagnetic armature 2 and a ferromagnetic movable element 3 that together form a magnetic circuit, and the movable element 3 occupies a position relative to the ferromagnetic armature 2 that depends on the magnetic flux within the ferromagnetic armature 2 and the movable element 3.

[0020] According to the present invention, the ferromagnetic armature 2 is divided into at least a first portion 2' and a second portion 2'' that are movable relative to each other, and one or more variable air gaps 4, 5 are provided between the first portion 2' and the second portion 2'' of the ferromagnetic armature 2.

[0021] At least one piezoelectric actuator 6, 7 is connected to the first part 2' and the second part 2'' of the ferromagnetic armature 2, and is shown to set one or more variable air gaps 4, 5 between the first part 2' and the second part 2''. Therefore, the dimensions of the air gaps 4, 5 change, thereby changing the reluctance of the actuator 1 (i.e., the resistance to magnetic flux), and as a result, a controllable bidirectional force is generated on the soft ferromagnetic mover 3 of the actuator 1.

[0022] As is clear from the figure, the ferromagnetic armature 2 is symmetric with respect to the central actuator axis 8 passing through the permanent magnet 9 from which magnetic flux lines are generated. The magnetic flux lines are transmitted in opposite directions through the mover 3 and through both poles 10, 11 of the ferromagnetic armature 2, and the mover 3 is located between the two poles 10, 11.

[0023] Most advantageously, the actuator 1 comprises two piezoelectric actuators 6, 7 on both sides of the mover 3, and the piezoelectric actuators 6, 7 are for controlling the air gaps 4, 5 between the first part 2' and the second part 2'' of the ferromagnetic armature 2. Preferably, the piezoelectric actuators 6, 7 simultaneously control the air gaps 4, 5 between the first part 2' and the second part 2'' of the ferromagnetic armature 2.

[0024] In the embodiment of FIG. 2, the second part 2'' of the ferromagnetic armature 2 is embodied as a relatively small stator element compared to the static main body forming the first part 2' of the ferromagnetic armature 2. The piezoelectric actuators 6, 7 are arranged between the static main body (i.e., the first part 2' of the ferromagnetic armature 2) and a relatively small movable stator element forming the second part 2'' of the ferromagnetic armature 2, which is smaller compared to the first part 2'.

[0025] It is further shown in both FIGS. 1 and 2 that a flexure 12 is applied to suspend the movable stator element of the second part 2'' of the ferromagnetic armature 2, while a flexure 13 is applied for the suspension of the mover 3.

[0026] Embodiments of the present invention can independently include any combination of the features disclosed herein. Although the present invention has been described above with reference to exemplary embodiments of the present invention, the present invention is not limited to this specific embodiment and can be modified in many ways without departing from the present invention. Therefore, the described exemplary embodiments should not be used to strictly interpret the appended claims. On the contrary, the embodiments are only intended to explain the language of the appended claims and are not intended to limit the claims to this exemplary embodiment. Therefore, the protection scope of the present invention should be interpreted only according to the appended claims, and the ambiguity that may arise in the language of the claims should be resolved using this exemplary embodiment.

[0027] Modifications and variations of the present invention will be apparent to those skilled in the art, and it is intended that all such modifications and equivalents be covered in the appended claims. The entire disclosure of all references, applications, patents, and publications referred to above is hereby incorporated by reference into this specification. Unless specifically stated as "essential" above, none of the various components or their interrelationships are essential to the operation of the present invention. Rather, desirable results can be achieved by substituting various components and / or reconfiguring their relationships.

Claims

1. A reluctance actuator (1) comprising a ferromagnetic armature (2) and a ferromagnetic movable element (3) that together form a magnetic circuit, wherein the movable element (3) occupies a position relative to the ferromagnetic armature (2) that depends on the magnetic flux within the ferromagnetic armature (2) and the movable element (3), the ferromagnetic armature (2) is divided into at least a first portion (2') and a second portion (2'') that are movable relative to each other, and one or more variable air gaps (4, 5) are provided between the first portion (2') and the second portion (2''), and at least one piezoelectric actuator (6, 7) is provided with the ferromagnetic armature (2 A reluctance actuator (1) is connected to a first part (2') and a second part (2'') of a ferromagnetic armature (2), and one or more variable air gaps (4, 5) are set between the first part (2') and the second part (2''), wherein the ferromagnetic armature (2) is symmetrical with respect to a central actuator axis (8) passing through a permanent magnet (9) that generates magnetic flux lines, the magnetic flux lines are transmitted through the movable element (3) and through both poles (10, 11) of the ferromagnetic armature (2) in opposite directions, and the movable element (3) is located between the two poles (10, 11).

2. The reluctance actuator according to claim 1, characterized in that the actuator (1) comprises two piezoelectric actuators (6, 7) on both sides of the movable element (3), and the piezoelectric actuators (6, 7) are for controlling the air gap (4, 5) between the first portion (2') and the second portion (2'') of the ferromagnetic armature (2).

3. The reluctance actuator according to claim 2, characterized in that the piezoelectric actuators (6, 7) simultaneously control the air gap (4, 5) between the first portion (2') and the second portion (2'') of the ferromagnetic armature (2).

4. The reluctance actuator according to any one of claims 1 to 3, characterized in that the second portion (2") of the ferromagnetic armature (2) and the movable element (3) are suspended by bent portions (12, 13).

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