WO1992008238A1

WO1992008238A1 - Process for producing an electromagnetic actuator and actuator so obtained

Info

Publication number: WO1992008238A1
Application number: PCT/FR1991/000854
Authority: WO
Inventors: Claude Oudet
Original assignee: Moving Magnet Technologies Sa
Priority date: 1990-10-29
Filing date: 1991-10-29
Publication date: 1992-05-14
Also published as: FR2668646B1; FR2668646A1

Abstract

Process for producing an electromagnetic actuator of the type comprising a stator structure in two parts (2, 3) defining between them a cylindrical air gap (4) in which moves a thin cylindrically-shaped mobile magnet (5). The stator structure (1) is coupled to at least one electrical field coil (6). The process according tothe invention consists in producing, firstly, a stator structure (1) by stacking together blanked sheet metal, and secondly, the electrical coil (6) surrounding a core (7), the unit so obtained being then slidingly inserted according to a longitudinal axis into a cavity (12) opening onto the air gap (4). The shape of said cavity (12) is adapted to the core (7) surrounded by its electric coil (6). The coupling of said core (7) to the stator structure is effected through the part of the core opposite the air gap (4). The invention also concerns an electromagnetic actuator comprising a core (7) having on its rear face (18), opposite the air gap, (4) coupling means co-operating with means in the stator structure (1), said means being movable only according to an axis perpendicular to the plane of the sheet metal. Applications in actuators for hard disk drives.

Description

Method of manufacturing an electromagnetic actuator and actuator thus produced.

The present invention relates to a method of manufacturing an electromagnetic actuator comprising a stator structure formed by two parts defining between them a cylindrical air gap in which a thin movable magnet of cylindrical shape moves. The stator structure is coupled to at least one electric excitation coil. Such actuators are in particular described in patent application PCT / CH / 87/00063 or patent application PCT 87/07757.

The invention consists in preparing on the one hand the stator structure, and on the other hand forming the electric coil around a core, the assembly thus produced is then introduced by sliding along a substantially longitudinal axis into a cavity s' opening onto the air gap. The shape of said cavity is complementary to the shape of the core provided with its electric coil. The core thus wound cooperates with the air gap, the connection between said core and the stator structure being effected by the part of the core opposite to the air gap.

This embodiment is particularly advantageous in that the different stages are easy to implement by simple and reliable tools, which makes it possible to significantly reduce the cost of manufacturing the actuators thus produced and to lend themselves to mass production. . In particular, winding around a free core is much easier to perform than placing a coil inside a stator structure having only a narrow slot for introducing the wire intended to form the winding.

According to a variant, a self-supporting coil is produced in a known manner, for example by winding wires coated with an ermoadherent envelope. The coil thus produced is then threaded onto the core. In this Indeed, the nucleus has three successive segments, of decreasing di-ïinsions when one moves away from the air gap. The first segment constitutes the central pole of the stator structure, the second segment of section less than or equal to the section of the central pole constitutes the core of the coil and the third segment of lower section constitutes the means of magnetic and mechanical connections of the core with the stator structure.

The manufacturing method according to the invention also makes it possible to optimally reduce the distance between the central pole of the part of the stator carrying the. coil, and the side poles of the complementary stator part, which has the effect of significantly reducing the disturbances of the magnetic field occurring in these areas. Finally, the complementary means make it possible to very precisely define the width of the air gap at the level of the central pole.

Advantageously, the core provided with the coil is secured by bonding with the stator structure after positioning of the core in the stator structure.

Preferably, the core and the stator structure are formed by stacking sheets.

The present invention also relates to an electromagnetic actuator produced in accordance with the method which is the subject of the present invention. The actuator thus produced is characteristic in that the core has, at its rear face opposite the air gap, complementary connecting means with means provided in the stator structure, said means allowing movement along only a longitudinal axis. The longitudinal axis is defined in the context of this patent as the axis perpendicular to the plane of the sheets. The aforementioned complementary means provide on the one hand the magnetic seal between the core and the stator structure, and on the other hand the mechanical joining of the core with the stator structure allowing among other things to rigidly define the air gap at the central pole . Of preferably, the rear face of the core has a cylindrical protuberance having at least one diverging zone with respect to a median plane of symmetry.

By "cylindrical" within the meaning of this patent, it is meant any shape generated by the displacement of a generator along any continuous path, said path being able to present non-continuous changes in orientation. Thus, a protuberance whose cross section is trapezoidal will be considered to be cylindrical. Similarly, a parallelepiped is considered to be cylindrical.

According to an advantageous embodiment, the two parts of the stator structure arranged on either side of the slot corresponding to the air gap are connected only by two zones arranged on either side of said slot, the length said zones being less than 0.5 E, E denoting the width of the air gap.

Preferably, the length of the zones arranged at the ends of said slot is less than 1 millimeter, of the order of 0.5 millimeters. This embodiment makes it possible to maintain the field generated by the coil in the air gap, in the absence of a magnet, constant very close to the end of the air gap, and therefore to increase the stroke at constant torque of l mobile organ

Advantageously, the end of the slot is rounded.

According to a preferred variant, the air gap has at the level of the slot separating one of the lateral edges of the core and the corresponding edge of the stator structure an area in which the distance between the two opposite edges of the air gap is minimal. Advantageously, the edge of the air gap opposite to the slot separating one of the lateral edges of the core and the corresponding edge of the stator structure has a protuberance substantially symmetrical with respect to the longitudinal plane passing through said slot, said protuberance having a substantially equal length. to E and a width maximum at most equal to 0.1 E, E denoting the width of the air gap.

In addition to the ease of manufacture of such actuators and their reduced manufacturing cost explained above, the actuators according to certain particular embodiments have advantageous performances.

The actuators according to the invention make it possible in particular to obtain a maximum stroke with minimal bulk in the direction of movement of the mobile member. This reduced size can be obtained even when the magnet manufacturing process requires a non-optimal magnet and air gap thickness. Such conditions arise for example for applications such as head arm arm motors for computer hard disk drive.

In the actuators known in the state of the art, in particular described by the abovementioned PCT patents, the stroke at constant torque remained clearly less than the width of the poles, and at best approached the width of the poles when the width of the The air gap was very small, provided that it is not always easy to check for problems with the manufacturing process of the thin magnet. In all cases known in the prior art, the stroke is limited to the width of the poles reduced by half the width of the air gap. However, the torque ceases to be constant at the end of the path traveled by the mobile magnet. In practice, the travel of the movable magnet corresponding to a constant torque characteristic is limited to the width of the poles reduced by twice the width of the air gap, which led in the prior art to unacceptable dimensions for a race. useful imposed.

The presence of the areas which are the subject of the present embodiment makes it possible to significantly increase the useful stroke and consequently to reduce the size of the actuator according to the present invention. According to another variant, the edge of the air gap has at the level of the slot separating one of the lateral edges of the core and the corresponding edge of the stator structure at least one polar horn with a width at most equal to 0.1 E and of a length substantially equal to (EW) / 2, designating the length of said slot. These embodiments make it possible to increase the useful stroke of the movable member by compensating for the disturbances of the magnetic field caused by the slot separating the core from the stator structure.

The present invention will be better understood on reading the description which follows, based on the drawings in which: FIG. 1 represents a view of the actuator in cross section

- Figure 2 shows a view of the actuator in longitudinal section

- Figure 3 shows a view of a detail of Figure 1. The actuator shown in Figure 1 consists of a stator structure (1) formed of two parts (2) and (3) complementary defining between them an air gap ( 4). A thin magnet (5) in the form of a tile is movable inside the air gap (4). An excitation coil (6) surrounds a core (7) integral with one of the parts (2) of the stator structure (1).

The stator structure consists of a stack of low-loss iron-silicon alloy sheets. These sheets are joined using known techniques by gluing, riveting or welding along longitudinal lines. They are cut in a known manner in order to present openings (8 to 11) for the passage of the rivets, of centering pins and / or possibly of the screws for fixing the actuator on a support. Another cutout (12) corresponds to the location of the core (7) provided with its coil (6). This cutout (12) opens onto the cutout corresponding to the air gap (4). All sheets of a actuator have the same cutouts, and can therefore be produced industrially at a reduced cost. In addition, cutting techniques ensure high precision, making it possible to produce high-quality miniaturized actuators.

The core (7) is also made of low-loss iron-silicon sheets stacked and secured by gluing or any other known technique.

It is of course possible, without departing from the scope of the present invention, to produce a solid stator structure and a core, for example in an iron-nickel alloy sold by the company CREUSOT LOIRE under the name "ANHYSTER D". This choice will generally be reserved for large actuators rather than for very miniaturized actuators.

The core (7) has a front face (13) whose developed length corresponds approximately to the travel of the movable magnet. In the context of the present patent, the term "length" means a dimension measured along the path of movement of the movable magnet and by "width" a dimension measured along an axis perpendicular to the plane of displacement of the movable magnet. The shape of the front face (13) of the core (7) corresponds to the shape of the air gap (4). We can distinguish three successive segments: the first segment (46) constitutes the central pole of the stator structure. The second segment (47) whose section is, in the example described, identical to the section of the first segment (46), constitutes the core and the support of the coil (6). The third segment (48), of a lower section, presets the attachment means allowing the attachment of the core (7) on the second part (2) of the stator structure (1).

The two lateral faces (14), (15) of the core (7) are substantially parallel to the plane 'of longitudinal symmetry (16) of the actuator. The rear face (18) has two lateral sectors (19, 20) substantially parallel to the front face (13), or at least parallel to a tangent to said front face (13). The rear face (18) also has a protuberance (21) allowing a sliding adjustment of the core (7) in the part (2) of the stator structure (1), and in particular makes it possible to introduce the core (7) to the when the actuator is assembled by translation along a longitudinal axis, and to limit or even prevent play on different axes. This protuberance (21) seen in section has a trapezoid shape, the small base of the trapezium being in the extension of the lateral sectors (19, 20) of the face, rear (18). The two lateral edges (22, 23) of the protrusion (21) diverge and constitute a sort of "dovetail". The winding (6) surrounds the side faces

(14, 15) of the core (7), the lower face (24) and the upper face (25) of said core (7). The winding (6) forms a rectangular frame, or slightly arched in the shape of a tile so as to optimize the volume occupied by the core provided with its coil and to keep the part of the copper parallel to the axis closer to the air gap, which is best to avoid the leakage flow. The realization of the coil in the form of a curved frame also makes it possible to increase the section of copper without changing the size along the plane of symmetry passing through the axis of rotation.

When the core (7) is placed in the stator structure (1), the front face (13). of the core (7) and the edges (26, 27) of the air gap are separated by two slots respectively (28, 29) of a selected length as small as possible, preferably less than 0.5 E and from the order of a few tenths of a millimeter. For example, the width E of the air gap is of the order of 2.6 millimeters, the thickness of the magnet being of the order of 1.6 millimeters and the unwound length of each pole on the order of 18 millimeters.

The movable magnet (5) consists of two parts (30) and (31) in the form of a tile, magnetized transversely in the opposite direction. This magnet can be made up of two magnets placed side by side, or by a single piece, two zones of which are symmetrical with respect to a median plane are magnetized in opposite directions. As shown in Figure 2, the movable magnet

(5) is integral with a movable member (32) pivoting about an axis (17). This mobile member is for example constituted by the arm of a rotary magnetic hard disk memory reader. The movable member (32) has a groove (33) in which the movable magnet (5) is embedded. The attachment of the magnet is completed by bonding. The arm is made of a light alloy or a composite material so as to have low inertia and high rigidity. The two parts (2 and 3) of the stator structure (1) are joined by two zones (34, 35) arranged at the two ends of the air gap (4). These zones have a length L of less than a millimeter so as to be saturated by a very small part of the flux of the magnet and to create an abrupt transition between the domain of constant magnetic field due to the current (without magnet) in the air gap. and the outside environment. The length of these zones (34, 35) is reduced to the minimum compatible with manufacturing tolerances, ie a length corresponding substantially to the thickness of the sheets, around 0.5 millimeter. Therefore the mobile magnet travels a path representing almost the entire race with a constant torque insofar as only the end of the race has a sudden transition causing a locking of the movable member. This locking phenomenon can be used to ensure stable positioning of the movable member in the absence of current, or can also be avoided by providing a blocking stop mechanically reducing the stroke of the movable member and preventing the coming of the magnet in the area in which the previously exposed magnetic field disturbance occurs. This stop can be made in the form of a thin cushion of flexible material extending one and / or the other of the zones (34, 35).

To improve the performance of the actuator, the ends of the air gap (4) have an area in which the width of the air gap gradually decreases. In the example described and illustrated in Figure 1, the ends of the air gap (36, 37) are rounded. One could also provide trapezoid-shaped ends, with a first zone for linear reduction of the width of the air gap, and a closing of the air gap in a plane perpendicular to the center line of the air gap.

Disturbances in the magnetic field caused by the magnet (30,31) occur at the slots (28, 29). To compensate for the disturbances created by the presence of these slots (28, 29), the edges of the air gap (4) have features visible in FIG. 3 representing a cross-sectional view on a scale 10 times greater than the scale used for Figures 1 and 2.

The edge (38) opposite the slot (28) has a protuberance (39) centered with respect to the longitudinal plane (40) passing through the axis of rotation (17) and the center (41) of the slot (28). The length L of this protuberance is substantially equal to the width E of the air gap. The maximum width 1 of the protuberance (39) is substantially equal to 0.1 E. This width varies regularly from a zero value at the ends to a maximum value at the center of the protuberance (39). On the opposite edge (41), the part (2) of the stator structure (1) has two pole horns (42 and 43) arranged on either side of the slot (28). L length P of each of the pole horns is substantially equal to (E-) / 2 and the maximum width p of the order of 0.1 E. Their shape corresponds substantially to the shape of the lateral parts of the protuberance (39) disposed symmetrically opposite. FIG. 4 represents an alternative embodiment in which the section of the core of the coil is less than the section defined by the product of the width of the central pole by the thickness of said central pole. As the core of the coil very rarely reaches saturation, it is possible to reduce the width of the core (7) at the level of the winding (6) in order to have a coil having a larger section of copper providing more ampere-turns for the same applied power, or to reduce the dissipated power for the given number of ampere-turns. The core (7) present in the embodiment presently described a first segment (46) whose section corresponds as previously to the section of the central pole, a second segment (47) of lower section intended to receive the coil (6) and a third section (48) of lower section comprising the mechanical attachment means and magnetic seal. In the first case, the torque and the efficiency of the actuator are increased, and in the second case, its electrical consumption is reduced. The latter case is particularly advantageous for actuators intended for hard disk drives installed in portable computers powered by accumulators.

The actuator shown in Figure 4 differs from the actuator previously described in that the coil

(6) is formed in a groove (44). This embodiment also differs from the actuator described above by the presence of a cut copper ring (44), and in the case described bent like the coil (6). This ring (44) is removable and is positioned on the core (7) at the time of assembly, before winding the coil (6). This ring (44) gives the electrical circuit a reduced electrical time constant.

The present invention is of course not limited to the above embodiment. On the contrary, a person skilled in the art will be able to carry out the invention in various forms without leaving the part of the present invention. In particular, the movable member may be of the linear displacement type, the air gap and the magnet in this case being plane symmetry. The dimensions, embodiment of the various constituents of the magnet actuator as well as the choice of materials can also be the subject of numerous variants.

Claims

R E V E N D I C A T I O S.

1 - Method for manufacturing an electromagnetic actuator of the type comprising a stator structure (1) formed of two parts (2), (3) defining between them a cylindrical air gap (4) in which a thin mobile magnet (5) moves cylindrical in shape, the stator structure (1) being coupled to at least one electric excitation coil (6), said method being characterized in that the stator circuit (1) is produced on the one hand and that on the other hand, the electric coil. (6) placed around a core (7), the assembly thus produced is then introduced by sliding along a longitudinal axis into a cavity (12) opening onto the air gap (4), the shape of said cavity (12) being complementary to the shape of the core (7) provided with its electric coil (6), the connection between said core (7) and the stator structure (1) being effected by the part of the core opposite to the air gap (4).

2 - Method of manufacturing an electromagnetic actuator according to claim 1 characterized in that the core (7) wound is secured to the stator structure (1) after implementation by gluing.

3 - A method of manufacturing an electromagnetic actuator according to claim 1 or 2 characterized in that the core (7) and the stator structure (1) are formed by a stack of sheets.

4 - electromagnetic actuator produced in accordance with the process forming the subject of any one of claims 1 to 3 characterized in that the core (7) has at its rear face (18) opposite the air gap (4) means for additional connection with means provided in the stator structure (1), said means allowing movement along a longitudinal axis only.

5 - electromagnetic actuator according to claim 4 characterized in that the core (7) has a first segment (46) whose section corresponds to the section of the central pole, a second segment (47) of section less than or equal to the section of said first segment (46) and a third segment (48) of lower section, presenting the means of securing with the second part (2) of the stator structure.

6 - electromagnetic actuator according to claim 4 or 5 characterized in that the rear face (18) of the core (7) has a cylindrical protuberance (21) having at least one diverging zone along an axis perpendicular to the plane of symmetry (16) of the air gap (4).

7 - electromagnetic actuator according to any one of claims 4 to 6 characterized in that the sheets forming the stator structure (1) have a slot corresponding to the air gap (4), said slot (4) separating the two parts of the stator structure (1) which are connected only by two zones (34), (35) arranged on either side of said slot, the length of said zones being less than 0.5 E.

8 - electromagnetic actuator according to claim 7 characterized in that the length of the zones

(34), (35) disposed at the ends of said slot is less than 1 millimeter, preferably less than 0.5 millimeter.

9 - electromagnetic actuator according to any one of claims 4 to 8 characterized in that the air gap (4) has at the level of the slot (28, 29) separating one of the lateral edges (14, 15) of the core (7) and the corresponding edge of the stator structure (1) ^' an area in which the distance between the two opposite edges of the air gap (4) is reduced.

10 - electromagnetic actuator according to claim 9 characterized in that the edge of the air gap (4) opposite the slot (28, 29) separating one of the side edges (14, 15) of the core (7) and the corresponding edge of the stator structure (1) has a protuberance (39) substantially symmetrical with respect to the longitudinal plane passing through said slot (28, 29), said protuberance (39) having a length substantially equal to E and a maximum width at most equal to 0 , 1 E, E designating the width of the air gap (4).

11 - Electromagnetic actuator according to claim 8 or claim 10 characterized in that the edge of the air gap (4) has at the level of the slot (28, 29) separating one of the lateral edges (14, 15) of the core (7 ) and the corresponding edge of the stator structure (1) at least one pole horn (42, 43) with a width at most equal to 0.1 E and a length substantially equal to (EW) / 2, designating the length of said slot (28, 29).

12 - Electromagnetic actuator according to any one of claims 4 to 8 characterized in that the core (7) has a groove (44) in which the coil (6) is at least partially housed.