GB2065984A - Electric Stepping Motor for Time Pieces - Google Patents

Abstract

A step micromotor comprises a stator (6) made of a non- ferromagnetic material and a rotor made as two discs (1, 2) whose alternating magnetic poles face one another, the bearings of said rotor being arranged within the body of the stator. Annular rings (14, 15) carrying truncated "teeth" pointing radially inwards stop the rotor at specific annular positions when the winding of the stator is de-energised. The stator winding (8) can be made as a series of small circular coils or as a single solid coil whose shape is oval, triangular or some other out-of-round. <IMAGE>

Description

SPECIFICATION Electric Step Micromotor for Time Pieces This invention relates to a step micromotor which can be used as an electromechanical device for wrist watches equipped with a quartz oscillator or in other types of such watches.

It is an object of this invention to provide such an electric step micromotor for time pieces, wherein the skew of the rotor shaft bearings is practically eliminated without any additional adjustment.

Another object of this invention is to provide an electric step micromotor for time pieces, which possesses high efficiency.

One more object of this invention is to provide a step micromotor for time pieces, which can be assembled outside the time piece and mounted therein with minimum time and labour expenditures.

And, finally, an object of this invention is to reduce the sensitivity of the micromotor to external magnetic fields.

These and other objects are achieved in that in an electric step micromotor for time pieces, comprising a rotor rotating in bearings and made as two discs, where opposite alternating magnetic poles whose field is axially directed face one another, a stator whose control winding is placed between the rotor discs and a locking device for stopping the rotor in specific angular positions with respect to deenergized stator, according to the invention, the stator is made of a non-ferromagnetic material and said locking device is provided with a gear wheel arranged in the stray or scattering field of the rotor magnets near the butt end of the stator winding.

Such design permits reduction of influence of inaccuracies in assembly upon the motor torque, localization of the magnetic flux within the motor volume and decrease of effects of external magnetic fields upon the operation of the micromotor.

In one of the embodiments of a step micromotor the bearings of the rotor are located within the body of said non-ferromagnetic stator between the rotor discs.

Such an arrangement permits better accuracy of positioning of the rotor with relation to stator and reduction of the motor dimensions.

In another embodiment of a step micromotor the locking device is made as two gear wheels arranged symmetrically at opposite butt ends of the stator winding near the periphery thereof.

Such a design permits balancing of the rotor in the axial direction.

In still one more embodiment of a step micromotor said control winding is made as a single coil whose shape is symmetrical with respect to the rotor axis and differs from a regular circle.

Such a design permits reduction of the number of coils in the stator to one resulting in less labour consuming assembly process.

The invention will now be described with reference to a specific embodiment thereof, taken in conjunction with the accompanying drawings, wherein: Fig. 1 illustrates a longitudinal section view of a micromotor featuring a symmetrical rotor and a stator winding composed of several coils; Fig. 2 illustrates a plan view of a micrometer as in Fig. 1; Fig. 3 illustrates a longitudinal section view of a micromotor featuring an asymmetrical rotor and a stator winding composed of several coils; Fig. 4 illustrates a longitudinal section view of a micromotor featuring a symmetrical rotor and a stator winding comprising one coil; Fig. 5 illustrates a plan view of a micromotor as in Fig. 4; Fig. 6 illustrates one embodiment of a unit of a shaft of the rotor; Fig. 7 illustrates a longitudinal section view of one disc of the rotor featuring a ring magnet;; Fig. 8 illustrates a plan view of a disc of a rotor as in Fig. 7.

A step micromotor shown in Fig. 1 in a simplified form comprises a rotor which is essentially two parallel discs 1 and 2 made of ferromagnetic material and rigidly secured in any known manner on a shaft 3. Permanent magnets 4 whose magnetic field is directed axially are attached onto the surface of the disc 1 , facing the disc 2, along the periphery thereof and spaced equally from one another. Magnets 5 whose magnetic field is also axially directed are attached on the disc 2, on the surface thereof facing the disc 1 along the periphery of said disc 2 and spaced equally from one another. The number of magnets on the disc 2 is equal to that of the magnets on the disc 1.Magnets on the discs 1 and 2 are placed one against another so that their opposite poles face one another and alternate, that is the poles S of the magnets on the disc 2 are placed against the poles N of all, for example, uneven magnets on the disc 1 and, conversely, the poles N of the magnets on the disc 2 are placed against the poles S of all even magnets on the disc 1.

In the embodiment of Fig. 1 each of the discs 1 and 2 is provided with eight permanent magnets.

Fig. 2 shows the plan view of the upper disc 1 of the rotor of the micromotor, provided with magnets 4a...4h.

But the number of magnets can be different, as shown in Fig. 5 wherein a micromotorfeatures a rotor having four magnets on each disc. In any case each of the discs 1 and 2 has uniformly spaced along the periphery and alternating magnetic poles whose fields are axially directed.

A stator 6 is arranged between the discs 1 and 2 of the rotor. In the embodiment of Fig. 1 the stator 6 is essentially a disc shaped yoke 7 made of a non-ferromagnetic material, whose four openings arranged along the circumference at equal distance from one another hold flat roured coils 8 (Fig. 2). All four coils 8 are electrically coupled to one another, for example, in series and form a stator winding connected to the source of heteropolar pulses (not shown).

A metal non-ferromagnetic bush 9 is pressed in the central opening 7a of the yoke 7. Stone bearings 10 and 11 are pressed in this bush 9.

The shaft 3 of the rotor is fit freely in these bearings 10 and 1 1. A pinion 12 and a hub 13 are pressed on the extending ends of the shaft 3 from both sides of the stator 6. The pinion 12 serves to transmit the rotary motion of the rotor to the wheel system of the watch mechanism and, in addition, carries the disc 1 of the rotor which is secured on the pinion 12 by pressing.

Similarly, the hub 13 carries the disc 2 of the rotor also secured by pressing.

The bearings 10 and 11 of the rotor are, consequently, located in the body of the nonferromagnetic stator 7 between the discs 1 and 2 of the rotor.

The discs 1 and 2 of the rotor are enveloped with a clearance by a locking device which is essentially two wheels 14 and 1 5 made of a non retentive material and arranged symmetrically at opposite butt ends of the stator winding along the periphery thereof. The inner surface of the wheel 14 is provided with teeth whose number and pitch corresponds to the number of the magnets 4a...4h on the disc 1. The wheel 15 is made similarly. The wheels 14 and 1 5 are rigidly secured on the butt end of the yoke 7 of the stator 6 as shown in Fig. 1 and arranged radially and axially with respect to the magnets 4 and 5 on the discs 1 and 2 so that the rotor is magnetically balanced with the locking device. Each toothed wheel 14 and 1 5 is placed within the stray or scattering field of the rotor magnets.

Though Fig. 2 shows the stator 6 having a winding composed of four round coils 8, it is clear to all skilled in the art that the number of coils 8 can be either even or uneven.

In the embodiment of a micromotor of Fig. 3 one of the discs of the rotor, for example, disc 1 has no magnets at all. In this case the disc made of a ferromagnetic material closes the magnetic flux between opposite poles of adjacent magnets 5 on the disc 2. The locking device has but one gear wheel 14, whereas the wheel 1 5a has no teeth and can be made of either ferromagnetic or non-ferromagnetic material, for example, brass and coated with a thin layer of a material possessing weak magnetic properties for example, nickel or its alloys The wheel 15a is here a means for balancing the rotor magnetically and is placed at the disc carrying the magnets, in this case the disc 2. In all other respects the micromotor does not differ from the micromotor of Fig. 1.

Fig. 4 illustrates a micromotor wherein the stator winding consists one coil 1 6. This coil 1 6 is wound directly on the yoke 7 of the stator and the geometrical center C of said coil 1 6 lies on the axis 00, of the rotor. The coil 1 6, as shown in Fig.

5, in not round in plan (not a regular circle), its shape is formed by two thick parallel straight lines conjugated at both ends by thick arcs. The discs 1 and 2 of the rotor are each equipped with four magnets.

Such a number of magnets is dictated by the geometrical shape of the coil 16. Should the need arise, the non-round shape of the coil 16 may be different from that of Fig. 5, for example, triangular, oval or clover leaf. But their common feature is that the majority of wires are to be oriented radially. The rest of the micromotor featuring one non-round coil of Figs 4 and 5 is essentially similar to the motor of Fig. 1.

In any of the above described micromotors of Figs 1, 3 and 4 the bearings 10 and 11 of the shaft 3 of the rotor may be pressed directly into the central opening of the solid yoke 7 of the stator as in Fig. 6.

Referring to Fig. 8, a ring multi-pole magnet 1 7 can be mounted on discs 1 and 2 of the rotor in micromotors of Figs. 1 and 4 or on the disc 2 of the rotor of the micromotor of Fig. 3 instead of individual magnets. The ring magnet 17, as shown in Fig. 7, is secured, for example, by bonding to the surface of the disc 1 or 2.

Claims (5)

Claims

1. An electric step micromotor for time pieces, comprising: a rotor rotating in bearings and made as two discs having opposite magnetic poles facing one another, whose field is axially directed; a stator whose control winding is placed between the discs of the rotor; a locking device intended to stop the rotor in specific angular positions in relation to the deenergized stator, said stator being made of a non-ferromagnetic material and said locking device having a toothed wheel arranged in the stray or scattering field of the magnets of said rotor near the butt end of the stator.

2. An electric step micromotor as claimed in Claim 1, in which the bearings of the rotor are placed in the body of said non-ferromagnetic stator between the discs of the rotor.

3. An electric step micromotor as claimed in Claim 1, in which the locking device is made as two toothed wheels arranged symmetrically and near the opposite butt ends of the winding of the stator and along the periphery thereof.

4. An electric step micromotor as claimed in Claim 1, in which said control winding is made as a solid coil whose shape is symmetrical to the axis of the rotor and is not round.

5. An electric step micromotor substantially as set fourth in any one of the preceding Claims and as described herein above with reference to the accompanying drawings.