Linear actuator with improved magnetic stability and stripping force

Abstract

To provide an electromagnetic actuator having a moving range with stroke length c and having a stable position at least at one end of the stroke.SOLUTION: An electromagnetic actuator comprises: an armature which has length Hm in a Y-axis direction and a shape symmetrical to a Y-axis; and a fixed stator yoke 1 which supports an electric coil 2. A fixed permanent magnet 4 is placed between an electromagnetic armature and the electric coil, has length Ha in the Y-axis direction, and has an air gap in the Y-axis direction between a fixed yoke and the armature, where (Ha+c) has almost the same size as Hm, and the length of Hm is 0.9×(Ha+c)<Hm<1.1×(Ha+c). The electromagnetic actuator comprises two pole pieces which are integrally provided with the fixed yoke, and provided by extending in the Y-axis direction on both sides of the fixed permanent magnet, with length of Hph and Hpb.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a linear electromagnetic actuator with one or two stable positions that do not consume energy. These stable positions are achieved by at least one permanent magnet. More specifically, the present invention proposes an actuator whose ability to leave these stable positions by an electric current, known as the stripping force, is improved compared to the prior art. The present invention also proposes an actuator that allows for a larger linear stroke than the prior art solutions allow, allowing for savings in the size of the magnets used for a given stabilizing force.

[0002] This actuator can be applied, by way of example, to any type of automotive fuel circulation valve, such as an actuator for an air inlet or outlet valve, or for moving a transmission element. In general, any function that requires the maintenance of one or more stable positions without electrical current and that can leave these positions by electrical command can be applied to a solution with an actuator as described in the present invention. [Background technology]

[0003] Actuators in which stability is provided by one or more magnets are known in the prior patent art.

[0004] For example, U.S. Patent Publication No. 4,779,582 proposes an actuator topology for moving automotive valves that uses magnets in the fixed (stator) portion that actively participate in maintaining the actuator's end positions. These magnets are positioned between two separate electrical coils to allow magnetic flux to loop around the first or second coil.

[0005] The same type of actuator topology can be found in European Patent Publication No. 0157632, or more recently in International Patent Publication No. WO 2014 / 023326.

[0006] The purpose of these devices is to solve the general problem of providing monostability or bistability without mechanical assistance such as springs, and without the consumption of electrical energy thanks to the use of permanent magnets.

[0007] However, these devices do not provide for easy release from the stable position because a spring is used to allow easier release, or stripping, from the stable position. Current in the coil can assist stripping in the preferred direction of circulation, but it cannot completely cancel the holding force generated by the magnet or generate sufficient stripping force to overcome the friction or load applied to the moving part.

[0008] Additionally, the use of two separate coils on either side of these centrally located magnets makes the actuator ineffective because half of the total windings are not magnetically activated when the moving part is at one end or the other of the actuator's stroke.

[0009] Another type of monostable or multistable actuator is also known from document WO 2004 / 066476, which is able to maintain these stable positions by the action of magnets supported on the moving part of the actuator.

[0010] This actuator is an advancement over the previous actuators in part because the entire electric coil participates in the force generation regardless of the position of the moving part throughout the stroke. In addition, the developed topology allows the generation of a stripping force that can be maximized by embedding magnets in the moving part according to the mathematical equations disclosed in this document.

[0011] On the other hand, this actuator has a novel topology that requires space in the axial direction (the direction of movement), which becomes even larger when the required stroke is large. This is because, as can be seen in Figure 6 of this document, the axial space requirement of the actuator is at least equal to twice the stroke plus the space required to install the electric coils and ferromagnetic poles on the stator. In addition, it can be criticized that the moving magnets are subjected to high accelerations due to the impact of the moving part's arrival at the extreme positions, which in the long term will be detrimental to the service life of the system.

[0012] Finally, actuator topologies in which the magnet is fixed within a magnetic structure, has bistable properties, requires only one electric coil to function in both actuation directions, and the moving part consists only of ferromagnetic pieces are also known, as described for example in applications WO 9427303 or WO 2015 / 114261. These topologies, by their nature, do not benefit from very large stripping forces, and it has been suggested to increase this force (stripping force) by using magnetic pole pieces.

[0013] Although this type of construction may partially solve the aforementioned problems (by using a fixed magnet and by using pole pieces), no precise teaching is given as to the use of pole pieces. In addition, the dimensional requirements given by these documents, and in particular by EP 0 713 604, produce actuators intended for small amplitude strokes of about + / - 1 millimeter as shown in its preamble.

[0014] Therefore, a need exists, not addressed by the prior art, to produce an actuator having the following characteristics: a stroke of a few millimeters, typically ranging from 15-20 millimeters, minimized magnet size, preferably having a stable holding force and sufficient net magnetic stripping force to resist friction and external loads applied to the moving parts of the actuator, and preferably having a significant actuation force over the stroke of the actuator. Summary of the Invention [Problem to be solved by the invention]

[0015] Disclosure of the Invention The present invention therefore aims to overcome the drawbacks of the prior art by proposing an actuator that has at least one stable position without electric current and makes it possible to realize a stroke of several millimeters while benefiting from an improved stripping force and maintaining limited axial space requirements.

[0016] Another object of the present invention is to allow the size of the magnet to be reduced compared to prior art embodiments in order to achieve a given stability force.

[0017] To achieve this, the present invention first proposes to break with the teachings of the prior art, and in particular those of EP 0 713 604, by providing a significantly different relative dimension between the height of the mobile mass and the height of the magnet, so that a person skilled in the art would not deviate from the dimensional ratios recommended here.

[0018] Secondly, the use of magnetic pole pieces is cleverly realized by, on the one hand, bringing these pole pieces close to the magnets of the actuator, and, on the other hand, providing a moving mass in a stable position.

[0019] Thirdly, and surprisingly to those skilled in the art, by using a fixed magnetic shim disposed between the magnet and the coil of the actuator and having substantially the same height as the height of the coil, it is possible to enhance the stabilizing force of the actuator without adversely affecting the stripping force generated by the electric coil.

[0020] More specifically, the present invention proposes a linear electromagnetic actuator having a stroke c and at least one stable position at one of the ends of the stroke. The linear electromagnetic actuator includes an armature made of a soft magnetic material, having a shape symmetric with respect to the Y-axis, capable of moving axially within the Y-axis, and having a length Hm in the Y direction, and a fixed stator yoke made of a soft magnetic material supporting at least one electric coil. The actuator further includes at least one fixed permanent magnet disposed so as to cross between the movable armature and the electric coil and magnetized across the X direction perpendicular to the Y direction. The magnet has a length Ha in the Y direction, and the fixed yoke and the movable armature are defined by at least one axial air gap therebetween, and Ha + c is on the order of the same magnitude as Hm, and the length of Hm is configured such that 0.9×(Ha + c) < Hm < 1.1×(Ha + c). Therefore, when the movable armature is within its extreme stable position, one of the two axial ends of the movable armature is close to one of the two axial ends of the permanent magnet.

[0021] "Stroke" within the meaning of this patent means the length of the movement of the movable armature along the axis Y between two axial stop portions that define the movement of the movable armature. These stop portions may be mechanical, may perform a magnetic function for a bistable actuator, or for a monostable actuator, one of the stop portions may be non-magnetic and the other stop portion may be magnetic.

[0022] In order to substantially increase the stripping force, particularly for long strokes of several millimeters, the actuator has two pole pieces fixed to the yoke, positioned on either side of the magnet and extending axially towards the magnet to heights Hph and Hpb, respectively.

[0023] Preferably, Hpb is close to c, and Hpb≧Hph.

[0024] In order to economize on the amount of magnets while benefiting from the increased force, both in terms of stripping force and magnetic stabilization force, the actuator comprises a shim made of soft ferromagnetic material inserted transversely between the permanent magnet and the electric coil.

[0025] The ferromagnetic shim has a length in the Y direction close to the length Ha of the permanent magnet, but preferably has a length close to the height of the electric coil so as to be close to the yoke.

[0026] Typically, an actuator has one or two stable positions. [Brief explanation of the drawings]

[0027] Other features and advantages of the present invention will become apparent from a reading of the following detailed exemplary embodiments with reference to the accompanying drawings. [Figure 1] 1(a) is an overall perspective view of a bistable actuator according to an exemplary embodiment similar to the second embodiment, and (b) is a partial cutaway view of the bistable actuator according to an exemplary embodiment similar to the second embodiment. [Figure 2] 1A is a view taken along an axial cross section of the bistable actuator according to the first embodiment of the present invention, illustrating one end position of each stroke, and FIG. 1B is a view taken along an axial cross section of the bistable actuator according to the first embodiment of the present invention, illustrating the other end position of each stroke. [Figure 3] FIG. 10 is an explanatory view taken along an axial cross section of a bistable actuator according to a second embodiment of the present invention. [Figure 4]FIG. 10 is an explanatory view taken along an axial cross section of a bistable actuator according to a third embodiment of the present invention. [Figure 5] 1 is a graph illustrating a typical force generated by a bistable actuator according to the present invention over a given linear travel. [Figure 6] 1A is a perspective view of a monostable actuator according to the present invention, and FIG. 1B is an explanatory view showing an axial cross section of the monostable actuator according to the present invention. [Figure 7] FIG. 10 is an explanatory view taken along an axial cross section of a bistable actuator according to a fourth embodiment of the present invention. [Figure 8] FIG. 10 is an illustration of a bistable actuator according to another embodiment of the present invention, taken along an axial cut plane. [Figure 9] 10 is a graph showing the effect of pole piece thickness. [Figure 10] 10 is a graph showing the effect of pole piece height. [Figure 11] 10 is a graph showing the importance of the relationship between the height of the magnet, the stroke and the height of the movable armature. [Figure 12] 7 is a graph showing a typical change in force for an actuator having an asymmetry such as that shown in FIGS. 6(a) and (b). [Figure 13] 5 is a graph illustrating the advantages achieved by the third embodiment of FIG. 4. [Figure 14] FIG. 10 is an illustration of another embodiment using magnetic shims without pole pieces. DETAILED DESCRIPTION OF THE INVENTION

[0028] FIG. 1(a) shows a perspective view of an actuator according to a specific embodiment of the present invention. In a typical embodiment, the preferred shape is axisymmetric about axis (A), with the actuator having a tubular shape. However, the present invention is not limited to this axisymmetric embodiment, as parallelepiped-shaped embodiments are also possible, as shown in FIGS. 6(a) and (b). Similarly, although the yoke 1 appears to be manufactured in two parts, this is merely an exemplary embodiment of how the outer yoke 1 may be manufactured.

[0029] The cutaway view of Figure 1(b), with one-quarter of the actuator removed to better reveal the details of the embodiment, includes all the components of the actuator in the preferred embodiment. Thus, the stator, which assembles the fixed portion of the actuator, features a yoke 1 made of a soft ferromagnetic material and having a cylindrical outer shape, an electric coil 2 housed in a cavity 3 formed in the yoke 1, and a permanent magnet 4 axially positioned in the center of the yoke 1. When asymmetry in the function of the actuator in one direction of movement or the other is desired, it may be envisioned that the magnets are not centered but offset axially. In this preferred embodiment, the yoke 1 extends axially, and within the area defined by the electric coil 2 are magnetic pole pieces 5b, 5h, adjacent to the magnet 4. The axially translatable portion of the stator consists of a tubular armature 6 made of a soft ferromagnetic material, which moves within the area defined by the magnet 4 and the pole pieces 5b, 5h. This armature 6 is fixed to a shaft 7. The shaft 7 slides in a bearing 8 fixed to the yoke 1 and serves to fix an external member (not shown) which is moved by the actuator.

[0030] The use of pole pieces 5b, 5h is not necessary for the basic part of the present invention, as shown in Figures 2(a) and 2(b). This is because, in the first embodiment of this bistable actuator shown in these figures, it is particularly recommended that the dimensions of the various elements constituting the actuator be such that they offer the possibility of creating linear strokes greater than those possible with prior art embodiments. Thus, if the axial height of magnet 4 is Ha, the axial height of movable armature 6 is Hm, and the stroke of the actuator is c, then it follows that Hm = Ha + c. This general dimensional rule, even if the equality is not strictly respected, makes it possible to create actuators with strokes c significantly greater than Ha. The height of the actuator, Ht, is therefore slightly greater than 2 × c + Ha. In other words, it is necessary to add the thickness of the axial stop 9 made of soft ferromagnetic material fixed to the yoke 1. This dimensional relationship results in the ends of magnet 4 being axially aligned or axially located near the ends of armature 6 when the armature is in its extreme position. This is an advantageous feature of the second embodiment shown in Figure 3.

[0031] It is noted that the armature 6 can be in contact with these axial stops 9, or with external stops (not shown), or with a non-magnetic element (not shown) inserted between the stops 9 and the armature 6. In fact, the object of the invention is to take advantage of the existence of a residual air gap Hg in axial height, the advantages of which can be seen in Figure 5, since the residual air gap can be positioned at a point on the stroke where the stripping force and the magnetic stabilizing force are optimized according to the needs of a given specification.

[0032] According to FIG. 11, an important feature of the relationship Hm = Ha + c can be understood. The reason is that the shown graph (FIG. 11) is a graph in which the factor X is changed such that X = Hm - (Ha + c). It is clear that the optimal stripping force when close to the position of -5 mm is the case where X = 0 in this example, and a significant decrease in the optimal value is observed when X becomes exactly negative or positive. Generally considered, the optimal stripping force was observed when 0.9×(Ha + c) < Hm < 1.1×(Ha + c). It was found that the decrease in the stripping force becomes significant as it deviates from this range.

[0033] FIG. 3 shows a second embodiment similar to the preferred embodiment shown in FIG. 1. Here, the elements of FIGS. 2(a) and (b) and the pole pieces 5b, 5h described in FIG. 1(b) are also illustrated. These pole pieces 5b, 5h are here arranged axially symmetrically with respect to the central plane of the actuator perpendicular to the axis of the actuator. These pole pieces 5b, 5h have a constant thickness Epc in the exemplary embodiments described here, and the force curve can be optimized by this value. The pole pieces 5h, 5b extend axially over heights Hph, Hpb such that their ends 10h, 10b are close to the magnet. In doing so, at each of the two stable positions of this actuator, there is also a close contact point between one of the two ends 10a, 10b and one of the two ends of the armature 6. The distances Hch, Hcb existing between the axial ends 10h, 10b of the pole pieces 5b, 5h and the axial ends of the magnet 4 may be equal if it is desired to give the actuator a symmetric behavior, in other words, the ability to have the same type of force response when activation occurs from one end of the stroke to the other or vice versa. It is also possible to give Hcb and Hch different values ​​if it is desired to give the actuator asymmetric characteristics (different force response between one direction of movement and another), or to manufacture a monostable actuator, such as that shown in Figures 6(a) and 6(b). Finally, it is also possible to integrate only one of these two pole pieces, or, if the yoke 1 is axisymmetric, to manufacture a pole piece that extends over a smaller angle, not exceeding 360 degrees. The latter modification makes it possible to specifically adjust the generated force as needed.

[0034] The use of the pole pieces 5b, 5h is particularly considered when the stripping force requirements are high, i.e. especially when the stroke of the actuator is increased, since the magnetic synergy between the armature 6 and the two pole pieces 5b, 5h results in high stripping forces and a significant increase in the overall mechanical work produced during the stroke.

[0035] For all embodiments using these pole pieces 5b, 5h, it is important to keep the values ​​of Hch and Hcb fairly small relative to the stroke c. We will now explain the function of these pole pieces 5b, 5h for the example of FIG. 3 when the armature 6 is in its lower stable position. Under the action of current, the magnetic flux generated by the coil 2 passes through the lower pole piece 5b and then through the armature 6. As a result, during the entire stroke, the heights Hph, Hpb are close to the stroke c, maintaining the passage of the magnetic flux. The relatively small thickness Epc compared to the radial thickness of the armature 6 ensures that the magnetic flux actually passes through the armature rather than quickly returning to the yoke 1. The lower pole piece 5b should therefore preferably have Hpb substantially equal to c. That is, Hcb has a small value compared to c or Hm. The upper pole piece 5h plays the role of an attractive force that assists stripping of the stable position due to the effect of the local variable reluctance between the armature 6 and the upper pole piece 5h. To adjust this stripping force, it is possible to follow, for example, the influence of Hch on the force curve as shown in Figure 9. The thickness Epc may also be given so that the stripping force and the force for the subsequent stroke can be varied according to predetermined specifications. To do this, the teaching of Figure 10 can be used as a general guide.

[0036] In general, the following is needed: The pole piece 5b facing the armature 6 is in a magnetically stable position where Hcb is small compared to c or Hm, i.e. Hpb is close to c. The pole piece 5b facing the armature 6 has Hcb≦Hch, making it possible to provide a favorable paced force by increasing Hch, for example by using a residual air gap Hg to adjust the magnetic stabilizing force, the stripping force and the force on the stroke. The thickness of the pole pieces is small and does not have to be constant relative to the radial thickness of the armature 6.

[0037] To improve the magnetic stabilization without current, it is preferable to place a magnetic shim 11 made of a soft ferromagnetic material radially between the magnet 4 and the coil 2. This shim 11 may have a height similar to the axial height of the magnet 4 as shown in Figure 7, or preferably a height similar to that of the coil, which ensures a favorable passage of magnetic flux between the magnet 4 and the yoke 1 as shown in Figure 4. Since excessive magnetic permeance of the coil 2, and therefore a short circuit of the effective magnetic flux between the magnet 4 and the coil 2, is undesirable, it is also preferable to optimize the thickness of the shim 11 by prioritizing the magnetic saturation of the shim.

[0038] This shim 11 allows the thickness of the magnet 4 to be reduced while maintaining the same mechanical characteristics (force generated by current, force without current). Consequently, by considering a magnet 4 of a given lateral thickness, or by considering the magnet 4 and shim 11 together to have equivalent lateral thicknesses, it is possible to obtain an actuator with the same total volume and the same size of the electric coil 2. A reduction in the magnet volume is optionally achieved in this way. This advantage and surprising property is shown in FIG. 13, where the change in the force curve with and without current (0 At and 100 At, respectively) is shown for two different actuators (the former with "0" and the latter with "1"), one without a shim and one with a shim behind the magnet. In the "0" case, the magnet 4 has a thickness of 2.5 mm, while in the "1" case, the magnet 4 has a thickness of 2 mm and the shim has a thickness of 0.5 mm, so the total thickness is equal to that in the "0" case. Despite the reduced magnet mass, the stripping force and magnetic stability are improved in the "1" case compared to the "0" case, regardless of the presence or absence of current. For the dimensional relationships in question and the magnetomotive forces and cross sections of the magnetic circuit present, it is necessary to adjust the relative thicknesses of the shim 11 and the magnet 4 in order to benefit from optimizing this effect.

[0039] The shim 11 may be used in conjunction with the pole pieces 5h, 5b as shown in FIGS. 4 and 7, or may be used without the pole pieces as shown in FIG.

[0040] A parallelepiped embodiment of the monostable actuator is shown in Figures 6(a) and (b). A notable feature is that the actuator is asymmetric and does not have the same force response in both actuation directions due to the special action of the pole pieces 5b and 5h. In the lower section, the distance Hcb is minimized to favor the proximity of the magnet 4 to the lower pole piece 5b, consistent with the teachings shown in Figure 3. To obtain the current-induced force that increases after the stripping force, as described in Figure 10, the distance Hch is greater than the distance Hcb. This actuator also has a non-magnetic stop at the top of the actuator, which also functions as a bearing 8. The armature 6 abuts against this element, resulting in no stabilizing force when the armature 6 is in the high position. The support for this stop 8 is shown here by a non-magnetic plate 12. Return to the low position may be achieved by the action of a current in the coil 2, gravity, or any external load. Figure 12 shows the behavior of such an actuator in the current-applied direction. It is clear here that the force curves at 100 At and -100 At are not symmetrical, and it is also clear that the curves without applied current are not symmetrical about the center of the stroke.

[0041] Generally, increasing the height Ha of the magnet improves the stripping force and the force on the stroke. For example, Figure 8 shows such an embodiment, where the force in the presence of current is increased compared to the embodiment shown in Figure 3, but the stroke c is reduced while maintaining a similar height Ht. This increase in magnet size is not, however, essential for the proper functioning of the actuator, and it is part of the objective of the present invention to have a practical function where the height Ha is substantially less than the stroke c and less than the height Hm of the armature 6.

[0042] The advantages and general teachings given to the actuator that is the object of the present invention are shown by way of example in FIGS.

[0043] In Figure 5, we show the variation of force over the stroke of the actuator as a function of the number of ampere-turns circulating in coil 2, from the perspective of a bistable actuator, when the dimensional criteria in Figure 3 are respected and pole pieces 5b and 5h are used. Here, we consider the case where Hcb = hcb = 0.5 mm, and Ha + c = Hm, with Ha = 10 mm, for a stroke c of ±5 mm, i.e., 10 mm. In this graph, FS denotes the magnetic stabilizing force, which is symmetrical on both sides; FA denotes the stripping force that allows the actuator to move away from the stable position with a non-negligible force; and FC denotes the force over the stroke that would be required if the actuator were to overcome loads (friction, recoil forces, gas forces, etc.) over the entire stroke. The thickness of the pole pieces is approximately 1-1.5 mm, i.e., small compared to the width of armature 6. Note that the direction of the current is, of course, important. That is, when the armature is at the -5mm position, a positive current results in an overall positive force that allows stripping depending on the insertion level, while a negative current increases the stabilizing force at this same position. On the other hand, when the armature is at +5mm, a negative current allows it to move away from the stabilizing position.

[0044] Figure 9 provides information about the dimensional relationship of the thickness Epc. As mentioned above, the thickness must remain optimized according to the established specifications. In this embodiment, as in the embodiment of Figure 5, an excessive increase in the value of Epc would ensure maximum stripping force, but would result in a significant reduction in the force during the second part of the stroke, which could even become negative, preventing operation under large external loads. Therefore, it is necessary to optimize the value of Epc, especially the cross section where the magnetic material is present, while maintaining a low value relative to the stroke. The use of a non-constant thickness Epc allows for a favorable compromise to be achieved due to the effect of magnetic saturation on the position.

[0045] FIG. 10 provides a suggestion for the value of Hch for optimum performance when specified such that Hcb=0.5 mm and Hm=Ha+c+0.5, so that when Hch=Hcb the end of the armature 6 is axially aligned with the end of the pole piece. This investigated case corresponds to a similar case to those shown in Figures 5-9, but we now show that increasing Hch relative to Hcb allows for a shift in the stripping force and the force on the stroke curve. If one wishes to prioritize stripping force, one must prioritize approximately equal values ​​for Hch and Hcb. If one wishes to benefit from increased force at the beginning of the stroke, one must prioritize a height Hch greater than Hcb, in other words, create an axial offset between the end of the attractive pole piece and the end of the armature 6. It should be noted that varying Hch and Hcb has only a negligible effect on the stabilizing force, since these parameters can be optimized independently of each other.

Claims

1. 1. An electromagnetic actuator having a range of movement of a stroke length c and having a stable position at least at one end of the stroke, an armature (6) made of a soft magnetic material, movable in the Y-axis direction, having a length Hm in the Y-axis direction and a shape symmetrical with respect to the Y-axis; a fixed stator yoke (1) made of soft magnetic material and supporting at least one electric coil (2); At least one fixed permanent magnet (4) magnetized in the X-axis direction perpendicular to the Y-axis direction; The fixed permanent magnet (4) is disposed between the electromagnetic armature (6) and the electric coil (2) in the X-axis direction, and the length of the fixed permanent magnet (4) in the Y-axis direction is Ha; An air gap is provided between the fixed yoke (1) and the armature (6) in the Y-axis direction, The rotor comprises two magnetic pole pieces (5h, 5b) located on both sides of the fixed permanent magnet (4) in the Y-axis direction, integrally connected to the fixed stator yoke (1), and extending in the Y-axis direction toward the fixed permanent magnet (4), The pole pieces (5h, 5b) extend in the Y-axis direction toward the fixed permanent magnet (4) and have lengths Hph and Hpb, respectively, and the ends (10h, 10b) of the pole pieces (5h, 5b) in the Y-axis direction closely face the side surfaces of the inner periphery of the fixed permanent magnet (4), and the length Hpb is substantially the same as the stroke length c in the Y-axis direction, and Hpb>Hph; a gap distance Hch, Hcb between the end portion (10h, 10b) of the magnetic pole piece (5h, 5b) and the side surface of the inner circumferential portion of the fixed permanent magnet (4) is smaller than the stroke length c, and the gap distance Hch and the gap distance Hcb satisfy Hch>Hcb; A linear electromagnetic actuator characterized in that (Ha+c) is approximately the same size as Hm, and the length of Hm satisfies 0.9×(Ha+c)<Hm<1.1×(Ha+c).

2. A linear electromagnetic actuator as described in claim 1, characterized in that, of the spacing distance Hch and the spacing distance Hcb, a stop portion is provided on the spacing distance Hch side.

3. A linear electromagnetic actuator as described in Claim 2, characterized in that the stop portion is provided at the top, is non-magnetic, and has the function of a bearing.

4. The linear electromagnetic actuator according to any one of claims 1 to 3, characterized in that the fixed permanent magnet (4) is magnetized in the X-axis direction, the inner peripheral portion of the fixed permanent magnet (4) has one of the N pole and the S pole, and the outer peripheral portion of the fixed permanent magnet (4) has the other magnetic pole.

5. 5. The linear electromagnetic actuator according to claim 1, further comprising a shim (11) made of a soft ferromagnetic material and arranged between the fixed permanent magnet (4) and the electric coil (2) in the X-axis direction.

6. 6. The linear electromagnetic actuator according to claim 5, wherein the shim (11) has a length in the Y-axis direction that is substantially the same as the length Ha of the permanent magnet (4).

7. 6. The linear electromagnetic actuator according to claim 5, wherein the shim (11) is disposed near the yoke (1) and has a length in the Y-axis direction substantially equal to the length of the electric coil (2).

8. 8. The linear electromagnetic actuator according to claim 1, wherein the linear electromagnetic actuator has two stable positions.

9. 8. The linear electromagnetic actuator according to claim 1, which has a single stable position.

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