The invention relates to a bistable electromechanical actuator.

In the prior art, various solutions are known for the bistable electromechanical actuators. Such a device is disclosed, for example, in the patent HU 230885. This document describes, among others, an electromechanical actuator, wherein the base member of the actuator comprises two permanent magnets, which are mounted to the base member with opposite polarity with respect to each other in a way that their magnetic axis define an acute angle. The shielding body is attached to the operating shaft pivotably around a stud in a way that the direction of the stud is perpendicular to the operating shaft. It means that within the housing of the actuator there is one electromagnet arranged in a secured manner, wherein in an idle state of the actuator, one end of the electromagnet resides adjacent to one of the two permanent magnets fixed to the base member. Upon applying DC voltage of appropriate polarity to the electromagnet, in response to the magnetic field developing in the electromagnet, the base member slightly pivots around the stud and a locking pin formed on the base member tilts out of its locked state from the locking groove. Then due to the magnetic fields, the base member displaces along a straight section of guiding elements, while the operating shaft of the actuator is moving together with it. When the locking pin of the other permanent magnet reaches the other locking groove, then due to the magnetic fields, said locking pin tilts into the other locking groove and gets locked therein in a stable manner. The drawback of this solution is that because of the construction of the actuator, the relatively large gap between the magnetic core of the electromagnet and the permanent magnet, and consequently, a relatively large magnetic force is to be generated by the electromagnet for moving the operating shaft. As a result, in the locked state the magnetic force between the permanent magnet and the cooperating stationary electromagnet will be too large and thus the releasing effect will not be safe enough. It is a further problem that for exerting large magnetic forces, substantial strength of current has to be provided in the coils of the electromagnet, which can cause overheating of the device after multiple subsequent operations, which further deteriorates the operational safety. It is an object of the present invention to provide a bistable electromechanical actuator which eliminates the above mentioned problems. The above objects are achieved by providing an actuator comprising:

- an operating shaft arranged in a housing, configured to move along its longitudinal direction, and having one end outside the housing,

- a base member attached to the other end of the operating shaft inside the housing, said base member being slidably coupled to at least one guiding element secured to the housing,

- wherein said guiding element has two locking grooves with a predetermined distance therebetween and a straight guiding section between the locking grooves for guiding the base member, said guiding section being parallel to the longitudinal direction of the operating shaft.

A tiltable unit is pivotably coupled to the base member wherein a permanent magnet is secured to the bottom side of the base member at its central part, and wherein said tiltable unit has two end portions having the same magnetic pole which is opposite the pole of the permanent magnet facing towards the inside of the housing; and wherein said tilting unit further comprises locking elements configured to lock in the locking grooves. Two electromagnets are arranged within the housing in a way that in an idle state of the actuator, one end of the magnetic core of either electromagnet is arranged adjacent to the permanent magnet and one end of the magnetic core of the other electromagnet is arranged adjacent to one end portion of the tiltable unit.

The above objects are further achieved by providing an actuator

- an operating shaft arranged in a housing, configured to move along its longitudinal direction, and having one end outside the housing,

- a base member attached to the other end of the operating shaft inside the housing, said base member being slidably coupled to at least one guiding element secured to the housing,

- wherein said guiding element has two locking grooves with a predetermined distance therebetween and a straight guiding section between the locking grooves for guiding the base member, said guiding section being parallel to the longitudinal direction of the operating shaft. A tiltable unit is pivotably coupled to the base member wherein a permanent magnet is secured to the bottom side of the base member at its central part, and wherein said tiltable unit has two end portions having the same magnetic pole which is opposite the pole of the permanent magnet facing towards the inside of the housing; and wherein said tilting unit further comprises locking elements configured to lock in the locking grooves.

In this aspect of the actuator, only one electromagnet is mounted in the housing in a way that in an idle state of the actuator one end of a substantially U-shaped magnetic core of the electromagnet is arranged adjacent to the permanent magnet and wherein the other end is arranged adjacent to one end portion of the tiltable unit.

Various embodiments of the bistable electromechanical actuator according to the present invention will now be described in detail with reference to the drawings, in which

Figure 1 is a front view of a shielding body applied in a preferred embodiment of the actuator according to the invention.

Figure 2 is a perspective view of the shielding body illustrated in Figure 1.

Figure 3 is a bottom view of the shielding body shown in Figure 1 , wherein a permanent magnet is secured to the shielding body.

Figure 4 is a front view of the shielding body shown in Figure 3 with the permanent magnet.

Figure 5 is a front view of a preferred embodiment of the actuator according to the invention in a first end position with electromagnets under voltage.

Figure 6 is a top plan view of the actuator shown in Figure 5, according to the invention, in the first end position.

Figure 7 is a front view of the actuator shown in Figure 5, in accordance with the invention, in the first end position with voltage free electromagnets.

Figure 8 is the front view of the actuator shown in Figure 5, according to the invention, at the moment of release from the first end position.

Figure 9 is the front view of the actuator shown in Figure 5, according to the invention, after release from the first end position during of the guided movement towards the second end position. Figure 10 is the front view of the actuator shown in Figure 5, according to the invention, at the moment of locking in the second end position with electromagnets under voltage.

Figure 11 is a front sectional view of some parts of the actuator shown in Figure 5, in accordance with the invention, in the first end position with electromagnets under voltage.

Figure 12 is a front sectional view of some parts of the actuator shown in Figure 5, in accordance with the invention, at the moment of release from the first end position.

Figure 13 is a front view of another preferred embodiment of the actuator according to the invention in its first end position with a single electromagnet under voltage.

Figure 14 is a sectional view of the actuator shown in Figure 13 at the moment of release from the first end position

In the drawings like elements are always identified with like reference numbers.

In Figures 1 to 4, various views of a shielding body applied in an exemplary embodiment of the actuator according to the invention.

The shielding body 4 is formed as a plate, the end portions 2a, 2b of which, defined along a direction parallel to the operating shaft of the actuator, are bent by substantially 90 degrees. At the central part of the shielding body 4, a shaft hole 17 is formed equidistantly from the two end portions 2a, 2b, the direction of said shaft hole being perpendicular to the direction of the operating shaft. The shielding body 4 can pivot in both directions around a shaft mounted into the shaft hole 17, which will be described in detail later. The shielding body 4 is made of a magnetizable material, for example iron or an iron-containing alloy.

As shown in Figures 3 and 4, at the central part of the shielding body 4, a permanent magnet 12 is mounted to its bottom side in a way that one of its poles (in the Figures, the northern pole N) faces towards the shielding body 4. Since the shielding body 4 is made of a magnetizable material, the permanent magnet 12 magnetizes the shielding body 4 and thereby it forms a permanent magnetic field within the shielding body 4 and around it. As shown in Figure 4, the shielding body 4 conveys the magnetic field of the permanent magnet 12 into the end portions 2a, 2b, whereby the same magnetic polarity (in the Figures poles N) is generated in the end portions 2a, 2b of the shielding body 4, which always have opposite polarity with respect to the side of the permanent magnet 12 which are further from the shielding body 4. In Figure 4, this side has a southern pole S. In Figure 4 the main direction of the lines of the magnetic force is indicated by an arrow. The permanent magnet 12 may also be secured to the shielding body 4 with a polarity opposite to the polarity shown in the drawings, in which case the polarity of the end portions 2a, 2b of the shielding body 4 will also be reversed.

Due to the design of the shielding body 4 described above, it provides the permanent magnet 12 with much better magnetic shielding, which also allows more reliable operation and higher operational safety.

Figures 5 to 7 illustrate a preferred embodiment of the actuator according to the invention in front elevation view and the top plan view in a first locked end position.

The actuator comprises an operating shaft 7, which is arranged moveably along its longitudinal direction inside a rigid housing 1. A base member 16 is attached to the operating shaft 7, said base member being slidably attached to a guiding element 3 secured to the housing 1 through a shaft 5 that is perpendicular to the operating shaft 7. The housing 1 comprises at least one, but preferably two guiding elements 3 on either or both sides of the base member 16 and thereby both ends of the shaft 5 can be guided for the sake of more reliable operation.

The guiding element 3 has two locking grooves 8a, 8b with a predetermined distance therebetween along a direction parallel to the operating shaft 7. The guiding element 3 also has a guiding section 8c in a range between said locking grooves 8a, 8b for guiding the end portions of the shaft 5 projecting from the base member 16, said guiding section 8c being parallel to the longitudinal direction of the operating shaft 7. The lengths of the working path of the operating shaft 7 is defined by the distance between the locking grooves 8a, 8b formed at the ends of the guiding section 8c. It is obvious for those skilled in the art that attachment of the guiding element 3 to the base member 16 can be realized not only through the ends of the shaft 5, but for this purpose one or more studs can also be formed on the base member 16 that are capable of moving along the guiding section 8c of the guiding element 3.

The shielding body 4 is coupled to the base member 16, wherein the shaft 5, which is arranged through the base member 16, is also directed through the shaft hole 17. The permanent magnet 12 is secured to the shielding body 4 in a way that its magnetic axis is substantially perpendicular to the longitudinal direction of the operating shaft 7. Within this context the feature "substantially perpendicular" is to be interpreted in a way that in the idle state, when the shielding body 4 is slightly tilted, the magnetic axis of the permanent magnet 12 (i.e. the imaginary line connecting its two poles) and the operating shaft 7 defines an angle slightly different from the rectangle depending on the extent of tilt. In a temporary state after release, when the shielding body, while moving, is practically parallel to the operating shaft 7, the magnetic axis of the permanent magnet 12 is perpendicular to the operating shaft 7.

As the ends of the shaft 5 (or in other embodiments, the corresponding studs formed on the base member 16), lean on the straight guiding section 8c formed on the guiding element 3, thereby relieving the operating shaft 7. Consequently, a single aperture 9 on the housing 1 is enough for the operating shaft 7. As also shown in Figure 6, the gap between the side surfaces of the base member 16 and the guiding element 3 is so large that the base member 16 can move between the guiding elements 3 quite easily.

A longitudinal locking member 11 is fixed to the shielding body 4, preferably to its upper side, said locking member 1 1 being substantially parallel to the operating shaft 7 and having a respective locking element 15a, 15b at both ends thereof for locking into the locking grooves 8a, 8b, respectively.

In another embodiment of the actuator according to the invention (not shown in the drawings), the shielding member 4 and the locking member 11 are formed as a single tiltable unit. In this embodiment it is not necessary to apply a longitudinal plate as an upper part of the shielding body 4, instead the locking elements fitting into the locking grooves 8a, 8b of the guiding element 3 may be formed adjacent to the end portions 2a, 2b of the shielding body 4.

In yet another embodiment of the actuator according to the invention (not illustrated in the drawings), the tiltable element, for example the shielding body 4, is attached to the base member 16 not via the shaft 5, but by means of studs, each stud projecting outwards on either side of the tiltable element. These studs usually fit into the respective holes of the base member 16.

As a further option, the shielding body 4 may be made of a non- magnetizable material. In this case additional permanent magnets are to be secured to the end portions 2a, 2b of the shielding body so that they be arranged with opposite polarities with respect to the permanent magnet 12.

In the actuator shown in Figures 5 to 12, two electromagnets 13a, 13b are secured inside the housing 1 and arranged so that in the idle state of the actuator, one (inner) end of the magnetic core 14a of one electromagnet 13a resides adjacent to the permanent magnet 12, while an (inner) end of the magnetic core 14b of the other electromagnet 13b resides adjacent to one end portion 2b of the shielding body 4. The cores of the electromagnets 13a, 13b are supplied with opposite electrical polarities through the electrical wires 19, thereby the respective ends of the two electromagnets 13a, 13b always have opposite magnetic polarities.

The electromagnets 13a, 13b are mounted on a supporting frame 18 by means of fastening screws 20, said supporting frame preferably being made also of magnetizable material, whereby the supporting frame 18 directs the magnetical lines of force without obstacle for generating an optimal "closed" magnetic circuit through the magnetic cores 14a, 14b, the permanent magnet 12 and the shielding body 4.

In the locking end position shown in Figure 7, the operating shaft 7 is in a withdrawn position, and the shielding body 4 is in a somewhat tilted position, wherein a respective locking element 15b of the locking member 11 is stably locked in the locking groove 8b. When the electromagnets 13a, 13b get into a voltage free state, the magnetic cores 14a, 14b of the electromagnets 13a, 13b preserve their magnetic properties due to the permanent magnet 12 and the magnetic shielding body 4 (in particular their magnetized end portions 2a, 2b), thereby the magnetic attraction between the permanent magnet 12 and the shielding body 4, as well as the magnetic cores 14a, 14b will be maintained, which prevents the locking member 11 from moving out from the locking groove 8b.

Figure 8 illustrates the actuator according to the invention at the moment of release from the first end position. At this time, a reverse polarity voltage is applied to the wires 19, resulting in the reversal of the magnetic polarities of the electromagnets 13a, 13b. Consequently, one electromagnet 13a starts repulsing the permanent magnet 12, while the other electromagnet 13b starts repulsing the proximal end portion 2b of the shielding body 4. Since the shielding body 4 can turn around the shaft 5, the locked end portion 2b of the shielding body 4 gets elevated, it leaves the locking groove 8b and then because of the magnetic repulsion the end portion 2b continues to elevate and as a result, the shielding body 4 tilts over into the other direction. This asymmetric orientation of the shielding body 4 is just enough for the electromagnets 13a, 13b to push the shielding body 4 to its other end position. The speed of the shielding body 4 can be slightly increased if the permanent magnet 12 and said end portion 2b of the shielding body 4 are in a somewhat offset position with respect to the electromagnets 13a and 13b towards the locking end portion 2b, because in this case after release the electromagnets 13a, 13b immediately start repulsing the whole shielding body 4 and pushing it towards the locking groove 8b.

After the release, the shielding body 4 moves in parallel to the direction of the operating shaft 7 in a guided manner due to the end of the shaft 5 leaning on the guiding section 8c of the guiding element 3, while together with the shielding body 4 the operating shaft 7 is also moving outwards.

Figure 9 illustrates the actuator according to the invention after its release from the first locked end position and in course of the guided movement into the other end position, wherein the shielding body 4 is oriented substantially symmetrically with respect to the two electromagnets 13a, 13b. At this time an attractive force is exerted to the free end portion 2a of the northern pole N of the shielding body 4 by the proximal electromagnet 13a, which, in turn, repulses the bottom side of southern pole S of the permanent magnet 12, while said bottom side is being attracted by the other electromagnet 13b. The other end portion 2b of the shielding body 4, which has been locked so far, is now repulsed by the proximal electromagnet 13b. Due to the resultant of these forces the shielding body 4 starts moving continuously towards the second locking end position. With appropriate dimensioning the duration of the transition between the two end positions is typically a few tenth seconds.

Figure 10 illustrates the actuator according to the invention at the moment of getting locked in the second locking end position. Now the shielding body 4 is tilted so that its other end portion 2a is approaching to the magnetic core to the respective electromagnet 13a, the locking element 1 1 tilts over together with the shielding body 4 and the respective locking element 15a gets locked in the locking groove 8a. In this locked state, after switching off the voltage of the electromagnets 13, the attraction between the permanent magnet 12 and the end portion 2a of the shielding body 4, as well as the magnetic cores of the electromagnets 13a, 13b is still maintained like in the first end position.

In the second end position, the operating shaft 7 is in an entirely projected position and the ends of the shaft 5 lean against the end wall of the guiding section 2c. Pressing the operating shaft 7 is prevented by the locking of the locking element 15a of the locking member 11 in the locking groove 8a.

Figures 11 , 12 schematically illustrate some parts of the above described embodiment of the actuator according to the invention in front sectional view in the first end position, and at the moment of release from the first end position, respectively.

In Figure 11 the arrows show the main direction of the magnetic fields developed in the shielding body 4, the permanent magnet 12 and the magnetic cores 14a, 14b of the electromagnets 13a, 13b. As it can be clearly seen in the Figure, at the moment of locking and also subsequently thereto the end portion 2b of the shielding body 4 is very close to the magnetic core 14b of the electromagnet 13b. Due to this small gap, the magnetic attractive forces are substantial, which results in a very stable locking of the locking member 11.

One of the advantages of the actuator according to the invention is that both in the locked idle state of the actuator, when the electromagnets 13a, 13b are in a voltage free condition, or at blocking and during the motion of the shielding body 4, when DC voltage of appropriate polarity is applied to the electromagnets 13a, 13b, the magnetic field of both poles of the permanent magnet 12 is utilized due to the specific design of the shielding body 4. As a result a substantially small gap may be applied between the permanent magnet 12 and the magnetic cores 14a, 14b of the electromagnets 13a, 13b, which at the same time, makes the release action particularly secure.

As shown in Figure 12, at the moment of release the repulsive force acting on the end portion 2b is very strong because of the small gap, thereby a large torque is applied to the shielding body 4, while in response to the repulsive force acting on the end portion 2b and the repulsive force acting on the permanent magnet 12, the shielding body 4 and the locking member 11 together tilt out of the locking position within a very short period and "jumps up" into the other locking position.

It is noted that by reducing or increasing the cross-section of the end portions 2a, 2b of the shielding body 4, the strength of the magnetic field developed therein can be changed, and the shaft hole 17 can be formed even in the locking members 11 instead of the shielding body 4.

In Figures 13 and 14, another embodiment of the actuator according to the invention is illustrated. This embodiment differs from the embodiment shown in Figures 5 to 12 in that this actuator comprises only one electromagnet 23, the magnetic core 24 of which is bent to a substantially U-shape in a way that its end portions 24a, 24b are arranged opposite to the permanent magnet 12 and either end portion 2a, 2b of the shielding body 4, thereby providing a relatively small gap. The two ends 24a, 24b of the magnetic core 24 always have opposite polarities, whereby the same arrangement of the magnetic poles is achieved as the arrangement including two electromagnets 13a, 13b and their straight magnetic cores 14a, 14b. The electromagnet 23 is mounted on a support frame 22, which is secured to the housing 1 by means of screws 22.

The advantage of the above described embodiment is that the electromagnet 23 can be formed as a flat unit, and thus the entire actuator can be very compact and can require little space, which is particularly beneficial in certain application fields, for example for safety locks and safes. In any embodiment of the actuator according to the invention it is particularly beneficial if the two arms of the shielding body 4 serving as a tiltable unit have the same length, i.e. the two end portions 2a, 2b are at the same distance from the center of the shielding body 4. In this case the locking elements 15a, 15b cannot be removed from the locking grooves 8a, 8b even by shaking or striking the actuator.

Another advantage of the actuator according to the invention is that its operational force and dimensions may be defined within a wide range while maintaining the optimal, power-saving and efficient operation, as well as reliability of the device. Due to this fact the electromechanical actuator according to the invention provides a much more reliable and more robust solution for a bistable locking than the currently widely spread cogged wheel- screw type actuators driven by electric motor.

The electromechanical actuator according to the invention can be preferably used in door locks, closing mechanisms and other locking devices, even under extreme conditions, that require two bistable end positions and a straight or substantially straight working path.