EP4740298A1 - Reluctance actuator - Google Patents

Abstract

Reluctance actuator (1) comprising a ferromagnetic armature (2) and a ferromagnetic mover (3), together forming a magnetic circuit, wherein the mover (3) occupies a position with reference to the ferromagnetic armature (2) which depends on a magnetic flux in the ferromagnetic armature (2) and the mover (3), wherein the ferromagnetic armature (2) is split into at least a first part (2') and a second part (2") that are movable with respect to each other so as to provide a variable airgap or air gaps (4, 5) between the first part (2') and the second part (2''), and that at least one piezo-electric actuator (6, 7) connects to the first part (2') and to the second part (2'') of the ferromagnetic armature (2) so as to set the variable airgap or airgaps (4, 5) between the first part (2') and the second part (2"), and the ferromagnetic armature (2) is symmetric with reference to a central actuator axis (8) through a permanent magnet (9) from which the magnetic flux lines originate that transmit in opposite directions through the mover (3) and through opposite poles (10, 11) of the ferromagnetic armature (2) between which opposite poles (10, 11) the mover (3) is located.

Description

Reluctance actuator

The invention relates to a reluctance actuator comprising a ferromagnetic armature and a ferromagnetic mover, together forming a magnetic circuit , wherein the mover occupies a position with reference to the ferromagnetic armature which depends on a magnetic flux in the ferromagnetic armature and the mover . https : / / www . engineeringsolutions . philips . com/ loo king- expert ise/high-preci si on- engineering/ comparative-evaluation- of-lorentz- and- reluctance- actuators/ discusses a comparative evaluation of Lorentz and reluctance actuators . It is discussed that Lorentz actuators (based on current carrying windings situated within a magnetic field) are widely used to achieve the highest level of force predictability . However, their limited force density result in significant heating of the coils and in local hot spots .

A signi ficantly higher force density and steepness can be achieved by reluctance actuators , which are based on attraction force exerted on a ferromagnetic mover by a ferromagnetic armature magneti zed by a coil . However , these latter actuators suf fer from larger paras itic ef fects , impacting their force predictability .

Such a reluctance actuator is further known from https : / / www . acin . tuwien . ac . at/en/proj ec t /hybrid- reluctanceactuator s- for-high-precis ion-mot ion/

In the reluctance actuator known from thi s website a permanent magnet and coils are used to generate magnetic fluxes through the ferromagnetic armature and the mover . The direction of the coil ' s flux i s the oppos ite of the magnet ' s f lux in one of the variable gaps between the mover and the armature . These fluxes cancel each other. Consequently, the total flux in one of the variable gaps is weaker than that in the other variable gap on the opposite side of the mover. The unbalanced flux on opposite sides of the mover results in a lateral actuation force on the mover .

It is an object of the invention to solve the problem of heat dissipation which is occasioned because of the current that is required to flow through the coils of the reluctance actuator for setting the mover in motion and keep it at a desired position. This problem is a hindrance for the reluctance actuator in replacing the usual Lorentz actuator, despite its advantages over the Lorentz actuator.

The article by Ueno T et al entitled "Linear step motor based on magnetic force control using composite of magnetorestrictive and piezoelectric materials", IEEE transactions on magnetics, USA, part 43, nr. 1, 19 December 2006 pages 11-14, XP011152115 discloses a composite of giant magnetorestrictive material (Terfenol-D) and a stacked piezoelectric transducer (PZT) actuator, as used in a linear step motor. The combination of a magnetic circuit with the said composite controls the magnetic force on the movable yoke with the voltage of the PZT's via mechanical stress.

The article by Ito S et al entitled "Long-range fast nanopositioner using nonlinearities of hybrid reluctance actuator for energy efficiency", IEEE transactions on industrial electronics, IEEE service center, Piscataway, New Jersey, USA, part 66, nr. 4, 7 June 2018, pages 3051 - 3059, XP 011703739 discloses a flexure guided nanopositioner with a nonlinear hybrid reluctance actuator for a large range and energy efficiency. The actuator has nonlinear negative stiffness that partially cancels the flexures' stiffness. The article by Pechacker A et al entitled " Integrated electromagnetic actuator with adaptable zero power gravity compensation" , IEEE transactions on industrial electronics , IEEE service center, Piscataway, New Jersey, USA, part 71 , nr . 5 , 26 June 2023 , pages 5055 - 5062 , XP 011956916 discloses an integrated electromagnetic actuator with a position independent zero power gravity compensation mechanism for variable masses . Gravity is actively compensated by a variable reluctance actuator with a seamlessly tunable electropermanent magnet . Counteracting the negative sti f fness of the variable reluctance actuator is done by application of Lorentz actuators to stabili ze the position of a magnetically levitated mover in two degrees of freedom .

According to the invention the reluctance actuator i s proposed to have the features according to any one of the appended claims .

In a first aspect of the reluctance actuator comprising a ferromagnetic armature and a ferromagnetic mover, together forming a magnetic circuit , and wherein the mover occupies a position with reference to the ferromagnetic armature which depends on a magnetic flux in the ferromagnetic armature and the mover, and wherein the ferromagnetic armature is spl it into at least a first part and a second part that are movable with respect to each other so as to provide a variable airgap or air gaps between the first part and the second part , and wherein at least one piezo-electric actuator connects to the first part and to the second part of the ferromagnetic armature so as to set the variable airgap or airgaps between the first part and the second part , the invention proposes that the ferromagnetic armature is symmetric with reference to a central actuator axis through a permanent magnet from which the magnetic flux lines originate that transmit in opposite directions through the mover and through opposite poles of the ferromagnetic armature between which opposite poles the mover is located . This avoids as much as possible nonlinearity of the reluctance actuator of the invention .

By using the piezoelectric actuators in the said manner as part of the reluctance actuator instead of coils to induce the required flux in the ferromagnetic armature , the reluctance of the actuator can be tuned and the mover can be directed to a required position . In other words : By actuation of the piezoelectric actuators , the dimensions change and therefore the reluctance of the actuator changes ( in other words the resistance to magnetic flux ) , resulting in a controllable bidirectional force generated on the soft ferromagnetic mover of the actuator .

In a preferred embodiment the actuator is provided with two piezo-electric actuators on oppos ite sides of the mover , which piezoelectric actuators are for controlling the air gaps between the first part and the second part of the ferromagnetic armature .

Preferably the piezo-electric actuators simultaneously control the air gaps between the first part and the second part of the ferromagnetic armature .

In one embodiment it is preferred that the second part of the ferromagnetic armature , and the mover, are suspended by flexures .

The accompanying drawing, which is incorporated into and forms a part of the speci fication, illustrates an embodiment of the present invention and, together with the description, serves to explain the principles of the invention . The drawing is only for the purpose of illustrating invention and is not to be construed as limiting the invention .

In the drawing : figure 1 shows schematically a first embodiment of a reluctance actuator according to the invention, and figure 2 shows schematically a second embodiment of a reluctance actuator according to the invention .

Whenever in the figures the same reference numerals are applied, these numerals refer to the same or similar parts .

A reluctance actuator 1 as shown in the figures comprises a ferromagnetic armature 2 and a ferromagnetic mover 3 , together forming a magnetic circuit , wherein the mover 3 occupies a position with reference to the ferromagnetic armature 2 which depends on a magnetic flux in the ferromagnetic armature 2 and the mover 3 .

According to the invention the ferromagnetic armature 2 is spl it into at least a first part 2 ' and a second part 2 ' ' that are movable with respect to each other so as to provide a variable airgap or air gaps 4 , 5 between the first part 2 ' and the second part 2 ' ' of the ferromagnetic armature 2 .

It is shown that at least one piezo-electric actuator 6 , 7 connects to the first part 2 ' and to the second part 2 ' ’ of the ferromagnetic armature 2 so as to set the variable airgap or airgaps 4 , 5 between the first part 2 ’ and the second part 2 ’ ’ . Accordingly the dimensions of the air gaps 4 , 5 change and therefore the reluctance of the actuator 1 changes ( in other words the resistance to magnetic flux ) , resulting in a controllable bidirectional force generated on the soft ferromagnetic mover 3 of the actuator 1 .

As is clear from the figures the ferromagnetic armature 2 is symmetric with reference to a central actuator axis 8 through a permanent magnet 9 from which the magnetic flux lines originate that transmit in opposite directions through the mover 3 and through opposite poles 10 , 11 of the ferromagnetic armature 2 between which opposite poles 10 , 11 the mover 3 is located .

Most beneficial is that the actuator 1 is provided with two piezo-electric actuators 6 , 7 on opposite sides of the mover 3 , which pie zoelectric 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 piezo-electric 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 .

In the embodiment of figure 2 the second part 2 ' ’ of the ferromagnetic armature 2 is embodied as a relatively smaller stator element in comparison with a 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 the in comparison with the first part 2 ’ relatively small movable stator elements forming the second part 2 ’ ’ of the ferromagnetic armature 2 .

It is further shown in both figure 1 and in figure 2 that flexures 12 are applied to suspend movable stator elements of the second part 2 ’ ’ of the ferromagnetic armature 2 , whereas flexures 13 are applied for suspension of the mover 3 .

Embodiments of the present invention can include every combination of features that are disclosed herein independently from each other . Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention . The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith . On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment . The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exemplary embodiment .

Variations and modi fications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modi fications and equivalents . The entire disclosures of all references , applications , patents , and publications cited above are hereby incorporated by reference . Unless speci fically stated as being "essential" above , none of the various components or the interrelationship thereof are essential to the operation of the invention . Rather, desirable results can be achieved by substituting various components and/or reconfiguration of their relationships with one another .

Claims

1. Reluctance actuator (1) comprising a ferromagnetic armature (2) and a ferromagnetic mover (3) , together forming a magnetic circuit, wherein the mover (3) occupies a position with reference to the ferromagnetic armature (2) which depends on a magnetic flux in the ferromagnetic armature (2) and the mover (3) , wherein the ferromagnetic armature (2) is split into at least a first part (2' ) and a second part (2' ' ) that are movable with respect to each other so as to provide a variable airgap or air gaps (4, 5) between the first part (2' ) and the second part (2' ' ) , and that at least one piezo-electric actuator (6, 7) connects to the first part (2' ) and to the second part (2'' ) of the ferromagnetic armature (2) so as to set the variable airgap or airgaps (4, 5) between the first part (2' ) and the second part (2' ' ) , characterized in that the ferromagnetic armature (2) is symmetric with reference to a central actuator axis (8) through a permanent magnet (9) from which the magnetic flux lines originate that transmit in opposite directions through the mover (3) and through opposite poles (10, 11) of the ferromagnetic armature (2) between which opposite poles (10, 11) the mover (3) is located.

2. The reluctance actuator of claim 1, characterized in that the actuator (1) is provided with two piezo-electric actuators (6, 7) on opposite sides of the mover (3) , which piezoelectric actuators (6, 7) are for controlling the air gaps (4, 5) between the first part (2' ) and the second part (2^{, f} ) of the ferromagnetic armature (2) .

3. The reluctance actuator of claim 2, characterized in that the piezo-electric actuators (6, 7) simultaneously control the air gaps (4, 5) between the first part (2' ) and the second part (2^{, f} ) of the ferromagnetic armature (2) .

4. The reluctance actuator of any one of claims 1-3, characterized in that the second part (2^{, f} ) of the ferromagnetic armature (2) , and the mover (3) , are suspended by flexures (12;