WO1982000929A1 - Stepping motor,particularly for electronic watch - Google Patents

Abstract

The two pole pieces (9 and 10) which extend respectively above and below the cylindrical permanent magnet (7) constituting the driving part of the rotor, each have an opening of generally circular shape, but profiled and limited. by three radial sectors (17) extending towards the center in the plane of the pole pieces. Under the effect of alternating pulses traversing the coil, the pole pieces (9 and 10) are excited alternately in North pole and in South pole. By the particular arrangement of the sectors (17) and of the cutouts (16) which separate them, the equilibrium position of the rotor between the pulses is offset from that towards which it tends when the pole pieces are excited.

Description

 Stepper motor, especially for electronic watch.

The present invention relates to a stepping motor, in particular for an electronic watch, comprising a permanent magnet rotor having several pairs of poles with magnetization axes parallel to the axis of rotation and distributed around the latter, a stator provided an upper pole piece and a lower pole piece, each of these pieces being magnetically connected to one end of a core carrying a coil periodically traversed by current pulses, and each of them having polar sectors which extend radially opposite an axial face of the rotor.

Motors of this type are already known, in particular from patent FR 24 25 756. This known motor has tongues distributed around the axis of the rotor and the latter has two concentric rows of magnetization axes, one of which has two times more axes than the stator parts have tongues, while the other has as many axes as the stator parts have tongues. In this motor, the pulses are all of the same polarity and the rotor advances at each step by an angle corresponding to twice the distance between the magnetization axes.

Also known, by the patent and CH 613 359, stepper motors whose stator is formed by two pairs of pole pieces which extend one above the rotor and the others below. The pole pieces located face to face on the same side of the rotor are separated by a diametrical air gap and the two air gaps are oriented differently. In a motor of this kind, the pulses which excite the coil are of alternating polarity and the rotor advances at an angle equal to that which separates two axes of magnetization during each pulse.

We realized that it was possible to simplify the construction of stepping motors, especially for watches, while improving their efficiency and reliability by using a different arrangement of the rotor and pole pieces from those which were already known in the context of the known constructions and recalled above.

The object of the present invention is to produce an engine of this kind comprising the targeted improvement. For this purpose, according to one of its aspects which is considered essential, the stepping motor according to the invention is characterized in that the pulses are of alternating polarity, the number of sectors of each pole piece is equal to half the number magnetization axes of the rotor, and the pole plates are shaped so that the positions corresponding to the balance of forces between the rotor and the pole pieces, in the case where the coil is energized and in that where it is not excited, are rotated relative to each other. An embodiment and some variants of the subject of the invention will be described below, by way of example, with reference to the attached drawing, in which: FIG. 1 is a top plan view of the pole pieces and of the rotor, FIG. 2 a view in longitudinal section passing through the axis of the rotor, FIG. 3 a partial plan view, on a light scale greatly enlarged, showing the opening of the pole pieces in an alternative embodiment, FIGS. 4, 5 and 6 are partial plan views similar to that of FIG. 3 showing other execution variants, FIG. 7 is a sectional view along line VII-VII of the, fig. 6, on a still enlarged scale, illustrating a detail of this figure, FIG. 8 is a view similar to FIG. 3 showing another embodiment of the engine, and FIG. 9 also a plan view similar to FIG. 3, showing a final embodiment.

The general arrangement of the motor is shown in Figs. 1 and 2. The motor frame comprises an upper element 1, for example a brass bridge and a lower element 2 which may be constituted by a second bridge or by a frame element of the movement in which the motor is incorporated. The frame elements 1 and 2 each comprise a bearing 3 which supports one of the ends of the shaft of a rotor 4. This rotor comprises for example a shaft 5, the upper part of which forms a pinion and the lower part passes through two washers 6 and the disc 7 constituting the cylindrical magnet of the rotor. At its two ends, the shaft 5 has the usual pivots which are engaged in the bearings 3.

The frame elements 1 and 2 are connected to each other by two pillars 8, one of which is visible in FIG. 2. These pillars are also used to position a lower stator part 9 and an upper stator part 10, as well as a spacer 11 made of a non-magnetic material, for example brass. The spacer 11 and the pole pieces 9 and 10 are also fixed and centered by two pins 12, one of which is visible in FIG. 2 and by corresponding screws 13. The pillars 9 also serve to fix the upper deck 1 by means of screws 14 and spacing sockets 15. We will now describe, based on FIG. 1, the arrangement of the stator parts 10 and 9, as well as the arrangement of the cylindrical magnet 7 which constitutes the main part of the rotor. As can be seen in this figure, the two stator parts 9 and 10 are elongated flat plates made of a ferromagnetic material with high permeability and low remanence, one of which extends above the upper face of the magnet 7 and 1. other below its underside. The bent ends of these pole pieces located opposite the rotor, are shaped so that they can be connected to the ends of a magnetic core (not shown) which supports the excitation coil of the motor. It is an elongated coil, the same kind as that used in many types of stepper motors. This coil will be connected to the circuit of the timepiece so as to be periodically excited by pulses of current of alternating polarity, so that the pole pieces 9 and 10 each constitute alternately a north pole and a south pole during the passage of the pulses whereas between the pulses, they constitute masses of ferromagnetic material playing the role of an armature with respect to the permanent magnet of the rotor.

Each pole piece has, opposite a circular axial face of the magnet 7, a profiled opening of generally circular shape, the opening of the pole piece 10 being designated by 16 in the drawing. This opening delimits three interior sectors 17, of the same dimensions which are distributed at 120º from each other and which each cover approximately an angle of 60º, so that they provide between them three empty zones also of 60º of angular opening.

We also see in fig. 1, the indication of the polar zones of the magnet 7. In the position shown in this figure, three north poles are visible in the notches which extend between the sectors 17, while that three south poles are hidden by sectors 17.

More precisely, during the time intervals between the pulses, the rotor assumes a position of equilibrium due to the forces of attraction between its different polar zones and the parts of the pole pieces 10 or 9 which are in the vicinity. Thanks to the cutting or to the particular conformation of the sectors 17, this equilibrium position is different from that which is obtained if the pole pieces 9 and 10 are magnetized by the wise step of a direct current in the coil. Thus, during each pulse, the rotor undergoes a torque which puts it in rotation and by its inertia, it moves to the next neutral equilibrium position. To achieve this offset from the equilibrium positions, many different arrangements can be provided, including FIGS. 3 to 9 give examples.

According to fig. 3, the opening 18 of the pole piece 10, partially visible in this figure, has a circular shape coaxial with the magnet 7 and extends over a diameter very slightly greater than that of the magnet 7. This profiled opening has three sectors 19 which are arranged like sectors 17 but one of the edges 20 of which, instead of being radial, is cut obliquely at an angle α of a few degrees relative to the radial direction.

It is not necessary that the sectors cover exactly an angle of 60º and that the notches extend over angles identical to those of the sectors. Thus, fig. 4 shows a variant in which the pole piece 10 is seen with an opening 21 also centered on the axis of the rotor 7. This opening 21 has parts in the form of narrow slots which delimit three sectors 22 which are asymmetrical with respect to a radius passing through their center of gravity. As seen in the drawing, these sectors each extend over more than 60º. The rotor 7 is shown with apparent N and S poles in the face facing the pole piece 10 and the pole areas are delimited by dotted lines. The position which the rotor takes in the absence of current and which it occupies between the steps of the motor becomes a position of imbalance at the time of the pulse in the coil when the pole pieces 9 and 10 are transformed into poles ^, magnetic respectively N and S or S and N depending on the polarity of the pulse. The rotor 7 then turns one step in the direction of the strongest attraction caused by this asymmetry. During the next rest period, the S poles of the rotor came in place of the N poles and vice versa.

According to fig. 5, these are the circular edges of the opening 24 of the pole piece 10 which are indented, while the sectors 25 are symmetrical and each extend over an angle of 60º.

As shown in fig. 6 and 7, the opening 26 presented by the plate 10 in this variant comprises' sectors 27, one of the edges 28 of which is folded in the direction of the rotor. We see in fig. 7 that the homologous edges of the sectors of the pole piece 9 are also folded in the direction of the cylindrical magnet 7. -

Figs. 8 and 9 show embodiments which include new improvements compared to the embodiments envisaged until now. The general arrangement of the engine has the same structure and it can be seen in particular in FIG. 8 the periphery of the rotor 7 which is arranged between an upper pole piece 10 and a lower pole piece 9. Polar zones N and S designated by 31 are formed on the rotor 7 .. These polar zones determine six axes of magnetization parallel to the 'axis of the rotor, distributed 60 from each other and oriented alternately, the North and South poles succeeding each other on the upper face of the rotor, while poles of opposite names follow one another in the same way on its underside. The pole pieces are pla ques planes and their extreme edges extend in an arc coaxially with the rotor 7 a little beyond the periphery of the latter. As seen in fig. 8, the pole piece 10 has a profiled opening which firstly comprises a circular central part 30 σoaxial to the rotor and whose diameter is slightly less than the internal diameter of the pole areas 31. The profiled opening of the stator piece 10 has at in addition to three notches with parallel edges 32 which are distributed at 120º from one another and which extend obliquely outwards. Each of these notches 32 has an end with a curved edge which extends beyond the periphery of the rotor. The three notches 32 are of the same dimensions and all three open into the opening 30 in regions which are located 120º from one another. Their width is such that the polar sectors 33, of slightly asymmetrical shape, delimited by the notches 32 and by the central zone 30, extend over arcs which are slightly less than the arcs covered by two adjacent polar zones 31.

As for the pole piece 9, it has a profiled opening (30 '. 32') which has exactly the same shape and the same dimensions as the opening (30, 32) of the piece 10. It therefore also has a central zone 30 'circular and three notches with parallel sides 32'. As seen in fig. 8, the orientation of the notches 32 'is slightly different from that of the notches 32. Thus, the central opening ^. of the part 9 can be considered to be offset by a certain angle around the axis of the rotor with respect to the opening 30, 32. This offset is 30 in the embodiment described here.

It follows from this arrangement and from the fact that the crown segment covered by two adjacent polar zones of the rotor 7 is slightly less than 120º, than the motor shown in FIG. 8 is arranged so as to stop the rotor spontaneously in the absence of current in the coil in an orientation where it occupies a stable equilibrium position. This orientation is such that pairs of polar zones N, "are located approximately opposite the sectors 33 of the pole piece 10 and the pole piece 9. From such a position, the excitation of the stator necessarily causes the rotation So, for example, it is clear that, from the position of Fig. 8, if the stator is excited so that the pole piece 10 becomes a North pole, the pole areas S of the upper face of the the rotor will be attracted towards the center of sectors 33 while the polar zones N will be pushed back in. The rotor will therefore rotate counterclockwise as seen in Fig. 8. In a particular embodiment of a motor of this kind, each step of the motor can correspond to a rotation of an angle of 30º. However, by following the dimensioning of the openings 30, 32, one can also obtain steps of 60º in which case, at the end of each step, the polar zones S of the rotor come to occupy the location q occupied the N polar zones at the start of the step. In an embodiment of this kind, it is not absolutely necessary for the rotary offset of the opening 30, 32 of the pole piece 10 relative to the opening of the pole piece 9 to be 30º. It could also be different.

On the other hand, the provision shown being valid for one. rotor with six pairs of poles, it is obvious that a corresponding arrangement could also be imagined, for example with the rotor with four pairs of poles, in which case the opening 30, 32 should include a circular central zone similar to zone 30 and two diametrically opposite notches similar to the notches 32, 32 '.

Fig. 9 represents yet another form of execution. Here, the pole piece 10 again has a profiled opening 30, 32 which has exactly the same shape and the same arrangement as in FIG. 8. The rotor 7 has six pairs of poles for its part and we see in FIG. 9 the polar zones 31 alternately N and S of the upper face of this rotor. On the other hand, as regards the lower pole piece 9, the outline of which is the same as that of the piece 9 in FIG. 8, the profiled opening here has a central zone 30 'and two oblique notches 32' which are diametrically opposite but which, moreover, have the same shape and the same dimensions as the three notches 32 provided in the pole piece 10. Here also in the absence of pulses in the coil, the rotor spontaneously places itself in a stable equilibrium position in which two polar zones 31 are arranged symmetrically with respect to a polar sector limited by two adjacent notches 32 and 32 '. When the rotor reaches this rest position, one of the notches 32 'of the lower stator part 9 plays the role of. brake and stops the rotor in this locking position. In the rest position shown in fig. 9, it can be seen that two pole areas of the underside of the rotor which are respectively opposite the pole areas S3 and N3 are partially opposite the notches 32 '. This circumstance causes a strengthening of the stable and static balance already existing by the effect of the three notches 32 of the pole piece 10. The current pulses in the coil are of alternating polarity.

At the moment of the appearance of an impulse, if the piece 10 becomes an N pole and the piece 9 a S pole, we see that there is attraction between the polar zones S and the sectors 33 and on the contrary repulsion between the same sectors 33 and polar zones N. The torque is exerted counterclockwise. On the other hand, on the underside of the rotor, the polar zones opposite to the zones N1, S1 and N3 are zones SN and respectively S which are located opposite a polar zone S and like the polar zone S which is opposite to N3 is partially discovered by one of the notches 32 ', the effect of the crown sector which extends between the two notches 32' on the rotor is a torque which also acts counterclockwise. The rotor is rotated. It takes a step of 60º until reaching a new position of stable equilibrium. This rotational movement comprises a first unlocking part followed by a fall into the new stable position.

It will be noted that the functional conditions of FIG. 9 can also be produced if the pole piece 9 has a profiled opening which has a central zone 30 ′ and a single notch 32 ′. Finally, by judiciously determining the angular span of the sectors 33 relative to that of the polar zones N, S of the rotor, it is possible to create stable equilibrium positions sufficiently marked so that it is sufficient to provide a profiled opening on the 'one of the pole pieces 10 or 9, the other pole piece then being devoid of any opening and serving only to conduct the magnetic flux by making the air gap as small as possible between them and the underside of the rotor. The embodiments according to fig. 8 and 9 and their various possible variants make it possible to produce a stepping motor for a watch whose consumption is reduced compared to that of motors of the same kind already known. On the other hand, the manufacture and assembly of these motors are greatly simplified, so that their cost price is very low. While, in many previously known motors, the pole pieces have protruding parts and hollow parts, so that the air gaps are variable, the construction described above makes it possible to use pole pieces which are entirely planar, so than the air gaps can be reduced to the minimum value. In the various motors described, the rotor is placed after each pulse in a stable equilibrium position determined by the shape of the profiled openings and that of the sectors, while at the appearance of the next pulse, it. undergoes a torque which gives it a rotary acceleration causing it to rotate towards a neighboring dynamic equilibrium position. However, as the impulse ceases during the movement, it continues to the next stable equilibrium position. Thus, the operation of the stepping motor is ensured on a regular basis and the rotor is subjected to each pulse a torque which always drives it in the same direction.

As mentioned above, many other variants are possible for the arrangement and shape of the openings of the pole pieces. So, for example, instead of the circular magnet having a slightly smaller diameter than that of the openings 16, 18, 21, 24, 26 and 30, 32, it could also have a slightly larger diameter and the relative dimensions of the polar sectors and notches could be different from what is shown in the drawing.

With each pulse, the rotor rotates 60º, which corresponds to the angular spacing between two axes of magnetization.

Claims

CLAIMS 1. Stepper motor, in particular for electronic watch, comprising a rotor with permanent magnetization presenting several pairs of poles with magnetization axes parallel to the axis of rotation and distributed around the latter, a stator provided with a part upper pole and a lower pole piece, each of these pieces being magnetically connected to one end of a core carrying a coil periodically traversed by current pulses and each of them having polar sectors which extend radially opposite an axial face of the rotor, characterized in that the pulses are of alternating polarity, the number of the sectors of each pole piece is equal to half the number of the magnetization axes of the rotor, and the pole pieces are shaped so that the positions corresponding to the balance of forces between the rotor and the pole pieces, in the case where the coil is excited and in the one where it is not excited, are rotated relative to each other. 2. Motor according to claim 1, characterized in that the rotor has six magnetization axes, the poles of each axial face of the rotor being alternately South and North, and in that the pole pieces extend on the surface beyond the periphery of the rotor and each have a profiled opening situated opposite the rotor and delimiting three polar sectors distributed regularly around the axis of the rotor. 3. Motor according to claim 2, characterized in that the sectors of one of the pole pieces are at least partially superimposed on those of the other pole piece. 4. Engine according to claim 3, characterized in that at least two homologous sectors are asymmetrical in shape with respect to a radius passing through their center of gravity. 5. Motor according to claim 4, characterized in that said sectors have an edge slightly folded in the direction of the rotor. 6. Engine according to claim 4, characterized in that ^at, least one sector of one of the pole pieces is angularly offset relative to the homologous area of the other pole piece. 7. Motor according to claim 3, characterized in that the parts of each pole piece which extend beyond the periphery of the rotor have an asymmetry intended to create, in the absence of pulses in the coil, a position d 'rotor balance different from that which exists when the coil is energized. 8. Motor according to claim 1, characterized in that the pole pieces are fixed on either side of a nonmagnetic spacer which surrounds the rotor. 9. Motor according to claim 8, characterized in that the means for fixing said pole pieces to the spacer are combined with means for fixing two frame elements which carry the bearings of the rotor and which are arranged on either side. other of the said pole pieces. 10. Motor according to claim 1, characterized in that the pole sectors of the two pole pieces are of different shapes. 11. Stepper motor, in particular for electronic watch, comprising a rotor with permanent magnetization having on each of its axial faces several polar zones (N, S) which define in pairs magnetization axes parallel to the axis of rotation, regularly distributed around the latter, a stator provided with two pole pieces (10, 9) which each extend opposite one of said axial faces and are magnetically connected each to one of the ends of a core carrying a coil periodically traversed by current pulses, characterized in that at least one of said pole pieces (10, 9) has, opposite the rotor, a profiled opening which delimits pole sectors (33) the number of which is equal to half the number of magnetization axes, at least one of said sectors extending over an arc greater than that which is embraced by a polar zone. 12. Motor according to claim 11, characterized in that at least one of said sectors extends over an arc approximately equal to that which is covered by two adjacent polar regions of the rotor. 13. Motor according to claim 11 or claim 12, characterized in that said sectors are asymmetrical. 14. Motor according to claim 11, claim 12 or claim 13, characterized in that all the polar seeteurs are of the same shape and the same dimensions. 15. Motor according to any one of claims 11, 12, 13 or 14, characterized in that only one of the pole pieces (10) has a profiled opening which delimits the said sectors, while the other pole piece does not have no opening, opposite the rotor. 16. Motor according to one of claims 11, 12, 13 or 14, characterized in that one of said pole pieces has a profiled opening which delimits the said sectors, while the other has a profiled opening which delimits a number sectors smaller than that of the first opening. 17. Motor according to one of claims 11, 12, 13 or 14, in which the two pole pieces each have a profiled opening, characterized in that said profiled openings are of the same shape and the same dimensions, but are offset in rotation one in relation to the other. 18. Motor according to claim 17, characterized in that the offset angle of said profiled openings is approximately equal to half the angle corresponding to a pitch of the rotor.