ELECTROMAGNETIC ACTUATOR

Description

[0001] The invention relates to an electromagnetic actuator with a magnetic circuit comprising magnetic circuit elements.

[0002] In the prior art, there are actuators in which the mechanical stiffness of a solid-state joint (flexure) is partially or completely compensated by a negative stiffness of the actuator. This negative stiffness is caused by the attractive force of permanent magnetic areas. An electromagnetic actuator according to the prior art is disclosed, for example, in US 2017 / 261859 A1.

[0003] The flexure and actuator tolerances add up and must be kept within certain limits during the manufacturing process.

[0004] Manufacturing a flexure with consistent stiffness across production runs places high demands on mechanical tolerances, as the stiffness can vary cubically with the individual dimensions of the flexure. It is therefore often necessary to tolerate mechanical dimensions in the micrometer range to remain within the required stiffness limits.

[0005] As soon as permanent magnets are used in the design of an electromagnetic actuator, forces exist between the stator and rotor in the unenergized state. These forces manifest as "stiffness" during movements between the stator and rotor. The magnitude of this so-called passive actuator stiffness is strongly dependent on the actuator's geometry, the tolerances of the air gaps, the magnet tolerances, and the specific magnetic resistance of the magnetic flux guide. Due to strong nonlinearities in the magnetic field, passive actuator stiffness, like flexure, exhibits a very high dependence on mechanical tolerances.

[0006] In an ideal system design, the stiffnesses of the actuator and the flexure are controlled to achieve a specific system behavior. For example, very low system stiffness allows for static operation with low power consumption. For dynamic operation, it can be advantageous to precisely set the system resonant frequency to a specific frequency for optimal control in the application.

[0007] The following generally applies to the resonant frequency of spring-mass systems: f res = 1 2 π c sys m

[0008] The mass "m" is usually given, constant, and cannot fall below a certain minimum value due to application requirements. Therefore, only the system stiffness remains to be adjusted for system resonance, which is composed of flexure and actuator stiffness as follows: c sys = c flexure + c actuator

[0009] State-of-the-art technology includes elements that influence system stiffness purely mechanically (e.g., lever arm changes, springs that can be locked along their length, individual mechanical post-processing, etc.). However, all these solutions place high demands on space requirements, complexity, and above all, require significant manufacturing effort.

[0010] A relatively flexible joint design within the desired range of motion has the disadvantage that parasitic stiffness is correspondingly soft. This highlights the advantage of targeted, partial compensation of the flexion stiffness by the actuator stiffness. The joint can then be designed to be relatively stiff overall, with the stiffness reduced only in the desired degrees of freedom by the opposing force of the permanent magnetic areas.

[0011] The object of the invention is to design and further develop the aforementioned electromagnetic actuator in such a way that it is simple in construction and inexpensive to manufacture. Furthermore, it should differ from the prior art and thus from competing products.

[0012] to avoid the disadvantages of very tight tolerances in the manufacture and operation of the actuators and to enable an easy-to-manufacture, cost-effective actuator with adjustable stiffness.

[0013] The problem is solved by an electromagnetic actuator according to claim 1. According to this claim, the magnetic circuit elements exert an attractive or repulsive force on each other, so that the actuator performs a movement, wherein at least one of the magnetic circuit elements is adjustable in its position relative to another magnetic circuit element to influence the actuator stiffness by means of an adjusting means, wherein the adjusting means is a mechanical means by which the position can be permanently or dynamically adjusted.

[0014] In principle, an electromagnetic actuator can consist of two magnetic circuit elements. A first magnetic circuit element can be in the form of a coil that generates a magnetic field as soon as current flows through it.

[0015] A second magnetic circuit element can be in the form of a permanent magnetic area, which consists either of a permanent magnet or a permanently magnetized area of ​​the actuator.

[0016] Even in this minimal configuration, when the coil is energized, a force can be exerted between the magnetic field generated by the coil and the magnetic field of the permanent magnet area. This force can be controlled by the current flowing through the coil. One could call this generated force the "controllable force," which constitutes the essence of the actuator: generating movement by controlling the force.

[0017] One could speak of a "static force" that represents the stiffness of the overall system. This static force is determined on the one hand by the mechanics of the actuator and on the other hand by the static magnetic force (generated by permanent magnets). If the actuator does not contain a third magnetic circuit element, the static magnetic force is zero, since no magnetic force acts when no current flows.

[0018] According to the invention, a third magnetic circuit element (permanent magnetic area or magnetically conductive material) is therefore essential. Through the interaction of the second and third magnetic circuit elements, a "static" force is generated by the static magnetic field acting between the magnetic circuit elements, resulting in a stiffness that (due to the non-linear distribution of the magnetic field) depends on the distance between the second and third magnetic circuit elements. Thus, by adjusting the distance between the second and third magnetic circuit elements, the actuator stiffness, and consequently the overall stiffness of the system, can be adjusted.

[0019] An electromagnetic actuator essentially consists of a magnetic circuit with magnetic circuit elements that serve to generate, guide, or amplify magnetic flux. The interaction of these magnetic circuit elements in a suitable arrangement exerts a force that ultimately results in movement. Magnetic circuit elements can be coils, permanent magnet sections, or magnetically conductive elements, which can be arranged in a variety of ways depending on the actuator type and application. For each specific application, it is always necessary to find the right configuration with regard to power requirements, space requirements, desired range of motion, and other specifications. A common feature of all these configurations is the combination of a coil, a permanent magnet, and a magnetically conductive material. The central element of this invention is the ability to selectively influence the actuator's stiffness.

[0020] The invention relates to actuators with a first magnetic circuit element in the form of a coil which generates a magnetic field as soon as it is traversed by current.

[0021] Furthermore, the actuator contains a second magnetic circuit element in the form of a permanent magnet section. This permanent magnet section can consist of a permanent magnet or a permanently magnetized area of ​​the actuator. The permanent magnet section can be located either in the stator ("hybrid reluctance actuator") or in the rotor of the actuator ("Lorenz actuator").

[0022] The magnetic field of the first magnetic circuit element (coil) can be controlled in strength and direction by the current intensity and direction. As soon as a current flows through the first magnetic circuit element, it exerts a force on the second magnetic circuit element, which can be attractive (with suitable polarity or paramagnetism) or repulsive (with appropriate polarity or diamagnetism).

[0023] Furthermore, the actuator contains a third magnetic circuit element in the form of another permanent magnet section or a magnetically conductive material. This third magnetic circuit element serves to shape, guide, or amplify the magnetic field of the first or second magnetic circuit element. Through the interaction of the second and third magnetic circuit elements, the static magnetic field between them generates a static force that (due to the non-linear nature of the magnetic field) depends on the distance between the second and third magnetic circuit elements.

[0024] The overall system possesses a stiffness that is composed of actuator stiffness (essentially corresponding to the stiffness of the magnetic field) and mechanical stiffness (essentially corresponding to the stiffness of the flexure): c sys = c flexure + c actuator

[0025] The mechanical stiffness is predetermined and constant due to the actuator's design.

[0026] The actuator stiffness results from the static magnetic field that forms between the second and third magnetic circuit elements. If the third magnetic circuit element is also a permanent magnet, an attractive or repulsive force results depending on the polarity, and thus a negative or positive stiffness, respectively. If the third magnetic circuit element is a magnetically conductive, paramagnetic material, the resulting force is attractive.

[0027] The stiffness of the actuator can be adjusted according to the invention by providing an adjustable magnetic circuit element, the position of which is adjustable relative to the position of another magnetic circuit element.

[0028] By precisely adjusting the adjustable magnetic circuit element, the air gap in the magnetic circuit is changed and, due to the dependence of the force on the air gap size, set to a desired stiffness. The relationship between force F and the position z of the adjustable magnetic circuit element (or air gap) is not linear.

[0029] The first derivative of the force with respect to position corresponds to the actuator stiffness. c actuator , which from the position z depends on: dF dz = − c z actuator

[0030] This also applies analogously to the torque M as a function of the angle of rotation. φ : dM dφ = − c φ actuator

[0031] Due to the non-linearity of the magnetic field, the stiffness also varies depending on the position of the adjustable magnetic circuit element.

[0032] Depending on its arrangement within the actuator and its design, the adjustable magnetic circuit element can be the second magnetic circuit element (permanent magnetic area) or the third magnetic circuit element (permanent magnetic area or magnetically conductive material). The adjustable magnetic circuit element is designed so that its position relative to another magnetic circuit element can be adjusted using suitable adjustment means.

[0033] Electrical, pneumatic, thermal, or mechanical devices can be used as adjustment mechanisms, allowing for permanent or dynamic position adjustment. Mechanical adjustment mechanisms are particularly simple in design and therefore inexpensive and energy-efficient.

[0034] The simplest mechanical adjustment devices are, for example, washers of suitable thickness.

[0035] A more elegant solution is to use a guide in which the magnetic circuit element is guided and fixed with a clamping device, for example via a lateral clamping screw.

[0036] A screw can also serve as an adjustment element, with which the position of the magnetic circuit element is adjusted.

[0037] Position adjustment is particularly easy when the magnetic circuit element itself forms the adjustable component. For example, the magnetic circuit element has a thread, such as a fine thread. The adjustable magnetic circuit element can then be positioned using a nut, screw, or similar means that engages the thread. It is especially advantageous if the adjustable magnetic circuit element is rotatably guided within its mounting, such as the coil carrier, which has a corresponding mating thread, and is therefore adjustable.

[0038] The actuator stiffness can be set to a predetermined value during the actuator's manufacture. Alternatively, it is possible to adjust the actuator stiffness only during installation in the specific application. This may be necessary if the application's resonant frequency and the overall system's frequency change due to additional mass, such as a mirror mounted on a single- or dual-axis actuator, thus requiring a readjustment of the stiffness.

[0039] The adjustable magnetic circuit element could also be positioned electromechanically. This would allow for automated adjustment, for example, through automatic calibration during manufacturing or during operation. The adjustment could then be performed variably during operation. The actuator stiffness of the system, and thus its resonant frequency, could then be dynamically adjusted, for example, to optimize power consumption or to perform resonant scanning. Resonant scanning means that the actuator stiffness is controlled so that the actuator's resonant frequency corresponds to the fundamental frequency of the desired movement.

[0040] The adjustability is particularly advantageous for actuators that perform movement in two or more axes. Such actuators can, for example, perform a tilting movement around one axis or around two axes offset by less than 90° to each other. With these types of actuators, a zero position often needs to be set. Without adjustability, all mechanical elements, and especially the magnetic circuit elements, would have to be manufactured and arranged with extremely tight tolerances. It is significantly simpler and more cost-effective if the adjustment is performed during or after the actuator's manufacture by simply adjusting the position of at least one magnetic circuit element. This compensates for manufacturing tolerances in the mechanics (especially the flexure) and the actuator (magnetic stiffness) through the adjustment process.This means that the natural frequencies of the entire system can be specifically adjusted, even via manufacturing tolerances, and are therefore reproducible. This results in a reproducible power consumption of the actuator and consequently a consistently usable controller design.

[0041] Such actuators are used, for example, to direct light in specific directions ("Fast Steering Mirror"). A mirror is mounted on the actuator's moving element for this purpose. It is particularly advantageous if the moving element itself acts as a mirror through a suitable reflective coating, as this reduces the moving mass and achieves high dynamics.

[0042] The advantages of the actuator according to the invention are: Targeted adjustment of the system stiffness for the respective application. The system's natural resonance can be reproducibly adjusted across production batches. This reproducible adjustment of the natural resonance, even across manufacturing tolerances, results in consistent power consumption and a consistently usable controller design. Manufacturing tolerances in the flexure and actuator are largely compensated for during the adjustment process.

[0043] There are now various ways to advantageously elaborate and further develop the teaching of the present invention. For this purpose, reference should be made, on the one hand, to the claims subordinate to claim 1 and, on the other hand, to the following explanation of preferred embodiments of the invention with reference to the drawing. In conjunction with the explanation of the preferred embodiments of the invention with reference to the drawing, generally preferred embodiments and further developments of the teaching are also explained. The drawing shows Fig. 1 shows a schematic view of an embodiment of an actuator according to the invention, Fig. 2 shows a schematic view of a further embodiment of an actuator according to the invention, Fig. 3 shows a schematic view of a further embodiment of an actuator according to the invention, similar to that shown in Figure 1Fig. 4 shows a schematic view of a further embodiment of an actuator according to the invention, with a function similar to that in Figure 1 Fig. 5 shows a schematic view of another embodiment of an actuator according to the invention, similar to that in Figure 4 Fig. 6 shows a schematic view of a further embodiment of an actuator according to the invention, in further development to Figure 5 Fig. 7 shows a diagram illustrating the force between the permanent magnet and the actuator core as a function of the distance between the permanent magnet and the actuator core. Fig. 8 shows a diagram showing the passive actuator stiffness as the first derivative of the distance between the core and the magnet. Fig. 9 shows a schematic view of a mechatronic system with actuators according to the invention. Fig. 10 shows a schematic view of the system consisting of Figure 9 In the tilted state, Fig. 11 shows a schematic view of the system. Figure 9with a permanent magnet area located in the stator at the base of the flexure, Fig. 12 shows in a diagram the typical torque curves of the actuator and the flexure as a function of the tilting of the system. Figure 9 and 10 Fig. 13 shows a diagram illustrating the compensation of actuator and flexure stiffness to achieve an overall system stiffness; Fig. 14 shows a schematic view of a system supplemented by another pair of actuators; and Fig. 15 shows a schematic, cutaway view of the system. Figure 14 .

[0044] Fig. 1Figure 1 shows an electromagnetic actuator 1 consisting of a coil 2, a core 3, and a permanent magnet 4 as the moving part. An attractive force exists between the permanent magnet 4 and the actuator core 3. Depending on the direction of current flow through the coil 2, this attractive force is either increased or decreased. Depending on the mechanical mounting of the permanent magnet 4, this results in a change in movement 5. The actuator core is designed to be adjustable in its position relative to the permanent magnet. The position is adjusted along the axis 6. The variable gap 7 between the magnet and the core provides a corresponding variable stiffness to the actuator.

[0045] In Fig. 2 is an actuator 1 similar to the one in Fig. 1shown, with the difference that now the core 3 represents the moving part of the actuator and the position of the magnet 4 is variable and is used for stiffness adjustment.

[0046] In Fig. 3 is an actuator as in Fig. 1 This is illustrated by the addition of a mechanical suspension, which serves as a solid-state joint and is indicated by spring 8. The mechanical stiffness of the solid-state joint is selectively partially or completely compensated (depending on the application and desired resonance frequency) by the actuator stiffness.

[0047] Fig. 4 shows an actuator which is basically like the actuator from Fig. 1 It works. The actuator core 3 is specifically implemented here as a cylinder with an external thread 9, which is located in a coil carrier 10 with a corresponding internal thread. The thread 9 allows for very fine adjustment of the distance 7 between the core 3 and the permanent magnet 4.

[0048] Fig. 5 shows an actuator as in Fig. 4 The difference is that the coil carrier 10, in which the actuator core 3 is adjusted, is made of a magnetically conductive material 11, just like the core 3. The magnetically conductive coil carrier 10 serves to reduce the magnetic resistance in the magnetic circuit and, accordingly, to increase the magnetic flux. This results in a greater actuator force for the same actuator power.

[0049] In Fig.6 is compared to Fig. 5 A further possibility is shown to reduce the magnetic resistance in the actuator 1 by using magnetically conductive material 11 to guide the magnetic flux past the coil back towards the moving part of the actuator.

[0050] In principle, there are various actuator configurations beyond the examples shown. For each application, it is always necessary to find the right configuration with regard to power requirements, space requirements, other specifications, and the desired range of motion. A common feature of all these configurations is the combination of a coil, a permanent magnet, and a magnetically conductive material. The central element of this invention is an adjustable component within the actuator to precisely control its stiffness.

[0051] The diagram in Fig. 7 shows an exemplary course of the force 12 between permanent magnet 4 and actuator core 3 as a function of the distance 7 between permanent magnet and actuator core.

[0052] Taking the first derivative over the distance between the core and the magnet yields the passive (coils unenergized) actuator stiffness 13 which in Fig. 8 is shown. c = dF dx c Actuator stiffness x Position of core to magnet F :Actuator force

[0053] The negative sign indicates that the force increases as the core approaches. The curve clearly shows the possible variation in stiffness depending on the core position.

[0054] Fig. 9 Figure 14 shows a specific mechatronic system that causes the tilting 15 of the moving element 16. The mechanical suspension is exemplified as a simple rod-solid joint 17. The actuator principle was derived from Fig. 4The design was adopted and applied symmetrically to both sides. To achieve a tilting motion, the two coils 2, 2' are each energized with opposite polarity. The coils 2, 2' are wound in the same direction, as indicated by the crosses 18 and dots 19. The respective distance 7, 7' between the magnetic circuit elements 3, 3' and 4, 4' is adjusted by means of a fine thread 9, 9' so that the overall stiffness of the system is optimized for the respective application.

[0055] Fig. 10 The mechatronic system is shown from Fig. 9 in a tilted state.

[0056] Fig. 11 The mechatronic system 14 shows Fig. 9with a permanent magnet area 4 located in the stator at the base of the flexure 17. The magnetic circuit closes, starting from the permanent magnet area (in this example, a permanent magnet 4), via the flexure 17 and the movable element 16 to the adjustable actuator core 3.

[0057] Fig. 12 shows the typical torque curves of the actuator ("M_actuator_0A") 18 and the flexure ("M_flexure") 19 as a function of the tilt 15 of the system. Fig. 9 10. A striking feature is the different sign between the actuator and the flexure, and thus the corresponding difference in sign in the stiffness. The curve "M_actuator_1A" 18' shows the torque when the actuator coils are energized with a current of 1 ampere.

[0058] In the diagram Fig. 13 The actuator and flexure stiffness compensate each other to form a total system stiffness ("M_system_0A") 20 according to the following formula: M system _ 0 A = M actuator _ 0 A + M flexure

[0059] Furthermore, the diagram shows that a coil current of approximately 1 A is required for a deflection of approximately 3°, which is indicated by the zero crossing 21 at 3° of the dashed curve "M_system_1A" 20'.

[0060] Fig. 14 Figure 22 shows a system 22 extended by an additional actuator pair rotated by 90°, which enables tilting about two spatial axes. The system has a mirrored area 23 on its upper surface. The mirrored area 23 can either be a mirror mounted on the movable element or be created by appropriately mirroring the movable element itself.

[0061] In the cross-sectional view Fig.15The moving part 17 with the permanent magnets 4, 4', 4", (magnet 4‴ not shown), the mechanical suspension in the form of a solid body joint 17 and the coil cores 3, 3', 3" (core 3‴ not shown), which can be varied in their position to adjust the stiffness, can be clearly seen again.

[0062] Regarding further advantageous embodiments of the teaching according to the invention, reference is made to the general part of the description and to the attached claims in order to avoid repetition.

[0063] Finally, it should be expressly pointed out that the exemplary embodiments of the teaching described above serve only to discuss the claimed teaching, but do not limit it to these exemplary embodiments. Reference symbol list

[0064] 1 Actuator 2, 2' Coil 3, 3', 3" Actuator core 4, 4', 4" Permanent magnet 5 Change in motion 6 Axis direction 7, 7' Variable gap 8 Spring 9, 9' External thread, fine thread 10 Coil carrier 11 Magnetically conductive material 12 Force profile 13 Actuator stiffness 14 Mechatronic system 15 Tilt 16 Moving element 17 Rod-solid joint, flexure 18, 18' Torque profiles of the actuator ("M_actuator_0A") 19 Flexure ("M_flexure") 20, 20' Overall system stiffness ("M_system_0A") 21 Zero crossing 22 Extended system 23 Mirrored area

Claims

1. An electromagnetic actuator (1) having a magnetic circuit comprising three magnetic circuit elements (2, 2', 10, 10', 11, 3, 3', 4, 4') and having an adjustment means, wherein the magnetic circuit elements exert an attracting or repelling force on one another so that the actuator effects a movement, wherein the position of at least one of the magnetic circuit elements relative to another magnetic circuit element is adjustable via the adjustment means in order to influence the actuator stiffness, wherein the adjustment means is a mechanical means via which the position is continually or dynamically adjustable.

2. The actuator according to claim 1, characterized in that the magnetic circuit elements are a combination of a coil (2, 2'), a permanent magnetic area (4, 4'), and / or a magnetically conductive material (10, 10', 11, 3, 3').

3. The actuator according to claim 1 or 2, characterized in that the first magnetic circuit element is designed as a coil, and is controllable via the current intensity and current direction in such a way that as soon as current flows through it, it exerts an attracting or repelling force, controllable via the current flow, on the second magnetic circuit element, which is designed as a permanent magnetic area.

4. The actuator according to one of claims 1 through 3, characterized in that the third magnetic circuit element is designed as a permanent magnetic area or as a magnetically conductive material, wherein the third magnetic circuit element is used to form, conduct, and / or intensify the magnetic field of the first and / or second magnetic circuit element(s).

5. The actuator according to one of claims 1 through 4, characterized in that due to the interaction of the second and third magnetic circuit elements as a result of the static magnetic field acting between them, a static force is generated that is a function of the distance between the two magnetic circuit elements.

6. The actuator according to one of claims 1 through 5, characterized in that a permanent magnetic area is present in the moving part of the actuator, and an actuator core (3, 3') is changed at a distance from the permanent magnetic area.

7. The actuator according to one of claims 1 through 6, characterized in that a magnetically conductive material is present in the moving part of the actuator, and a permanent magnetic area is situated at a distance from the moving part.

8. The actuator according to one of claims 1 through 7, characterized in that the permanent magnetic area is a permanent magnet or a permanently magnetized area.

9. The actuator according to one of claims 1 through 8, characterized in that the adjustment of the position of one of the magnetic circuit elements takes place by means of a thread (9, 9') and / or an electromechanical means.

10. The actuator according to one of claims 1 through 9, characterized in that the arrangement of the magnetic circuit elements is duplicated in a mirror-symmetrical manner in order to perform a tilting movement.

11. The actuator according to claim 10, characterized in that the arrangement of the magnetic circuit elements is duplicated with a rotation by 90°, as a result of which a two-dimensional tilting movement can be actuated.