CH631856B5 - Miniature motor for clockwork movement - Google Patents

Description

The present invention relates to a miniature motor for a timepiece movement, comprising a non-magnetic stator having a central cavity of predetermined dimensions, an annular carcass of high permeability and low remanence contiguously surrounding the stator, windings arranged at the inside the stator to create a magnetic field of determined direction when they are excited by the pulses of control current, a rotor comprising a shaft on which is mounted a permanent magnet having north and south poles, this rotor advancing step by step 180 ° at each excitation of the windings and being placed inside the central cavity.

Electric motors for watch movements are by their very destination very small members, generally having overall dimensions of the order of a few millimeters. Miniature motors for watches are already known, but most of them, if not all, present certain problems of assembly, disassembly, efficiency and torque.

Are known, in particular from the patents CH N ° 514181 and CH N ° 510293, electric motors for timepiece movements comprising a rotor with permanent magnetization, a stator winding without core provided with a support in non-magnetic material, and an annular cylinder head made of ferromagnetic material in which the stator is arranged so that in the absence of current the rotor takes a preferential orientation different from that of the plane of symmetry of the stator winding.

Patent CH 510 293 more precisely describes a miniature motor having two diametrically opposite screws screwed into the stator of the motor tangentially to the rotor in order to provide a preferential orientation of the latter in the absence of excitation. This is a special way of obtaining magnetization to stop the rotor.

Finally, FIGS. 58 and 58B of French patent 981 246 describe a motor comprising a magnet A2 which brings the rotor to a fixed direction, while a disk carrying paiers is mounted on the periphery of the stator; this motor comprises a stator, a rotor, an insulating material surrounding this stator and an external carcass, at least three windings being coated by the insulating material as well as the magnet.

The object of this invention therefore consists of a mini-i5 ture motor for a timepiece movement, comprising a non-magnetic stator having a central cavity of predetermined dimensions, an unnular carcass of high permeability and low remanence contiguously surrounding the stator, windings arranged inside the stator to create a magnetic field of determined direction when they are excited by the pulses of control current, a rotor comprising a shaft on which is mounted a permanent magnet having north and south poles , this rotor advancing step by step 180 ° at each excitation of the windings and being arranged inside the central cavity, this motor being characterized in that the stator comprises a coil body in one piece which has grooves longitudinal and transverse receiving the windings; in that two relatively rigid non-magnetic discs are fixed by their periphery to the internal surface of the stator to close the cylindrical cavity and thus define a chamber and to stiffen the motor assembly; in that these discs each comprise a central support coming in one piece with the disc and extending perpendicularly out of the disc on the side opposite to the cavity, these supports constituting the bearings of the rotor shaft; in that the carcass is cylindrical and is fixed to the coil body, and in that two pole pieces of high permeability and low remanence are fixed on the inside wall of the carcass but outside the windings, these two pieces being distant 40 from the rotor and extending parallel to its shaft so that they establish a magnetic polarization only when one of the poles of the rotor comes close, in order to stop the rotor at a determined position relative to the normal of the magnetic field produced by the windings.

45 According to a particular embodiment of the motor according to the invention, the device forming the poles comprises two diametrically opposite soft iron rods which are attached to the internal wall of the annular carcass and arranged at an angle to the normal to the direction of the magnetic field 50 to thereby form a polarization device intended to stop the motor in the same position after each excitation of the windings and to reduce the starting torque that the motor must develop when it receives a starting excitation.

The motor according to the present invention therefore comprises at least one ferromagnetic pole piece of high permeability and low persistence attached to the inner wall of the annular carcass external to the windings, this pole piece extending parallel to the shaft in order to establish a magnetic polarization 60 only when one of the poles of the rotor comes close to it, which is not the case of French patent N ° 981246, which does not concern a stepping motor, but a motor requiring the creation of 'a continuous field. Such a motor, moreover, if it was powered by pulses, would have a rotation of 360 and not of 180, this 65 being due to the magnet A2 forcing the rotor to make a full revolution between each pulse.

The motor described in the aforementioned French patent does not include a stator which includes a single piece coil having

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longitudinal and transverse grooves to receive the windings.

The windings are indeed not part of the stator,

but are embedded in the insulation and are therefore separated. This separation therefore requires a greater excitation current to generate an equivalent torque. In addition, in this motor, unlike the motor according to the invention, there is not found a relatively rigid closing disc comprising a bearing support extending perpendicularly to the latter with a bearing disposed at the end of this support.

The miniature motor according to the invention also has means for positioning the rotor different from those described in the three aforementioned patents, and comprises a bearing support and its bearing for the rotor shaft which is not described by any of these. patents.

One of the disadvantages of the engine of CH patent No. 510293 is mainly due to the fact of a much more expensive construction resulting from the use of screws and threads and a more complicated assembly. With the motor according to the invention, all these operations are not necessary: the pole piece is simply attached to the wall of the carcass by means of any adhesive, without any precise alignment being required.

The miniature engine according to the invention therefore presents, compared to the techniques known and revealed by the three cited patents, significant improvements in particular in the power consumption of its engine. For example, for an engine according to CH patent No. 510293, a power of several milliwatts would be necessary while the engine according to the invention requires only a few microwatts.

The characteristics of the miniature engine according to the invention will emerge more clearly from the description which follows with reference to the appended drawing, in which:

Fig. 1 is a perspective view with partial cutaway and on a large scale of an engine according to the invention:

fig. 2 is an elevational view taken roughly in the direction of the arrows 2-2 of FIG. 1, but on a smaller scale;

Fig. 3 is an elevational view taken roughly in the direction of the arrows 3-3 in FIG. 2:

Fig. 4 is a plan view and partially in section of one of the components of the engine according to the invention;

fig. 5 is an elevational view taken roughly in the direction of the arrows 5-5 of FIG. 4, and fig. 6 is a side elevational view, partially in section, taken roughly in the direction of the arrows 6-6 of FIG. 5.

The motor shown in the drawings is generally designated by 10 and consists roughly of a stator 11 and a rotating part 12. The stator comprises an annular yoke 13, a winding support or coil 14 forming at the same time the support of the motor assembly, the windings 15 and 16 and the flanges 17 and 18 in which the bearings for the shaft are formed. The rotating part 12 consists of a rotor 19, which may have the shape of a disc, and of a shaft 21 which is attached to the center of the rotor 19 by an adhesive, for example by an epoxy resin. The rotor 19 can be of any known magnetic alloy with high magnetization intensity and high permeability, for example an alloy of samari um and cobalt, and it is magnetized so that it has a north pole and a south pole at opposite ends of a particular diameter. An ordinary rod magnet can be used in some cases in place of a discoid magnet.

The coil 14, see also figs. 4, 5 and 6, is formed in one piece molded according to a preferred embodiment of the invention. It can be made of Nylon, polyvinyl chloride or any other synthetic material having sufficient dimensional stability and rigidity for this application. The material must be non-magnetic and, in some cases, brass or aluminum can also be used, for example, although it is necessary in this case to anodize these metals to form an insulating surface in order to avoid short circuits in or between the windings finally placed on the coil.

The coil 14 is a generally cylindrical part having a central cylindrical cavity 22 for the reception of the rotor 19 with sufficient clearance between the wall of the cavity 22 and the external surface of the rotor 19. On one side of an imaginary axial plane (which is oriented horizontally in the example shown), the coil 14 has transverse grooves 23 and 24 (fig. 6) and longitudinal grooves 27 and 28 (fig. 5), while transverse grooves 25, 26 and longitudinal grooves 29 and 31 are formed in the part of the coil 14 located on the other side of this axial plane, that is to say on the part shown below in the figures and in particular in FIGS. 5 and 6. The grooves 23, 24 and 27, 28 together form a winding notch in which a winding 15 is formed or arranged (fig. 2), and the grooves 25, 26 and 29, 31 together form a second notch winding in which a winding 16 is formed or arranged.

The interior surfaces or bottoms 68, 69 and 71, 72 of the grooves 23, 24 respectively 25, 26 are parallel, as shown by 2c in FIG. 6, but the bottoms 32 and 33 of the grooves 27 and 28, see fig. 5, are inclined relative to each other and are in fact oriented tangentially to the cylindrical surface of the cavity 22. This obliquity of the bottoms 32, 33 of the grooves 27 and 28 makes it possible to accommodate a greater number of turns of 25 thread only in similar grooves having parallel bottoms. The increase in the useful winding space is clear from the comparison of the darker hatched parts 20 and the lighter hatched parts 30 in FIG. 2.

The obliquity of the bottoms 32 and 33 also makes it possible to approach the winding 30 more from the cylindrical wall of the cavity 22, therefore also from the outer surface of the magnetic rotor 19 disposed in this cavity. A magnetic circuit is thus obtained having less losses. The motor is therefore capable of developing higher torque or greater output power for the same input power. The grooves 29 and 31 also have inclined bottoms 34 and 35, and the winding notch formed by the grooves 25, 26 and 29, 31 can therefore also receive more turns for the reasons indicated above. The obliquity of the bottoms 32.33 and 34.35 makes it possible to accommodate 40 in the notches approximately 20% more turns than in the notches provided for so far in this type of motors.

The cylindrical cavity 22 is connected at each axial end to a circular recess 36, respectively 37 (fig. 6) which is intended to receive the discoid or cheek part 38, respectively 39 45 of the flange 17 respectively 18, as described in more detail in what follows.

The formation in the coil 14 of the winding grooves 23, 24 and 27, 28 respectively 25, 26 and 29, 31 leaves on the coil two parts 41 and 42 in the form of segments and so two parts 43 and 44 having in section transverse the shape of radial bosses. In the axial ends of the segments 41 and 42 are formed radial cutouts 47 and 48 for the reception of the ends 49 and 51 of connection pins 52 and 53. The enlarged ends 49 and 51 of the pins are force-fitted 55 into holes 54 and 55 formed in segments 41 and 42. The bosses 43 and 44 each have a hole 56 or 57 for the passage of fixing screws for the case where it is desired to fix the motor in this way.

The flange 17 comprises a sleeve-shaped part 58, 60 the discoid part or radial cheek 38 of large diameter which has already been mentioned and which is connected at right angles to the part 58 at one of its ends and, at the opposite end, an inner rim 59 of smaller diameter which constitutes by its central inner surface the bearing for one of the ends of the shaft 21. 65 Similarly, the flange 18 comprises a radial cheek 39 of large diameter, a sleeve-shaped part 60 which is perpendicular to this cheek, and a smaller inner rim 61 at the other end of the sleeve part 60 to support

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the other end of the shaft 21. Because the flanges or bearings 59 and 61 are located at the outer ends of the parts 58 and 60 in the form of a sleeve, the bearing points of the shaft 21 are very widely spaced one from the other, so that the shaft 21 is supported in a very stable and precise manner. The flanges 17 and 18 can be of any hard material, not magnetic and having great dimensional stability. The licensee has found that a material suitable for this application is an alloy of beryllium and copper. When the bearings 59 and 61 are made of such a material, it is not necessary to provide lubrication. Although lubrication can nevertheless be provided if desired.

During assembly, it is preferable to first mount the rotor 19 on the shaft 21 and then place them in the cavity 22 of the coil 14. Then slide the flanges 17 and 18 on the shaft 21 so that the cheeks 38 and 39 fit into the recesses 36 and 37 at the ends of the cavity 22. After that, beads 62 (fig. 1) are deposited of a synthetic material, which may be the same as that of the coil, on the outer edges of the cheeks 38 and 39 and on the parts of the cylindrical wall of the recesses 36 and 37 located on the segments 41 and 42. The cheeks 38 and 39 are thus firmly connected to the coil 14 and form with that -this a relatively rigid structure which ensures precise and solid retention of the shaft 21. After assembly of the coil 14, the rotor 19, the shaft 21 and the flanges 17 and 18, the windings are wound 15 and 16 in the corresponding notches. The windings 15 and 16 are wound in the notches formed by the grooves described and along the inclined bottoms 32, 33, 34 and 35 under the usual tension for wire used in such a motor, for example wire No. 55 ASW. It is possible to wind about 47.5 m of this wire in all, forming about 2200 turns in each of the windings 15 and 16; the resistance of the windings in this case is approximately 5.6 kQ. The winding tension has the effect that the internal wall of the cylindrical cavity 22 is applied firmly against the outer edges of the cheeks 38 and 39, so that a monolithic structure is actually obtained. The windings surrounding the cheeks 38 and 39 contribute considerably to the rigidity of the assembly. Fig. 2 shows that the windings 15 and 16 are connected by a strand of wire 63 and that the ends 64 and 65 of the windings are placed transversely in the notches 66 and 67 formed in the ends 49 and 51 of the connection pins 52 and 53.

The recesses 36 and 37 (fig. 6) connecting to the ends of the cylindrical cavity 22 are located sufficiently inside the bottoms 68, 69 and 71, 72 of the transverse grooves 23 to 26 so that the layer of the windings 15 and 16 located furthest inward is slightly away from the outer surfaces of the cheeks 38, 39, which avoids the possibility of short circuits.

The assembly formed by the rotor, the coil and the windings is surrounded by the annular yoke 13. The latter has the form of a cylindrical envelope having a longitudinal or axial dimension which is equal to or slightly greater than the longitudinal dimension of the coil 14. On the internal wall of the annular yoke are fixed two diametrically opposed rods 45 and 46 made of soft iron which are arranged in a diametral plane making an angle a with the normal to the axis of the field created by the windings. These rods form poles constituting a device producing a force to stop the rotor at a determined position. The rods 45 and 46 can be attached to the annular yoke 13 in any suitable manner, for example by welding, gluing with an epoxy resin, or in another way.

The inside diameter of the annular yoke 13 is only slightly larger than the outside diameter of the spool 14, so that the yoke can be mounted with a very tight fit on the spool. The cylinder head carrying the rods 45 and 46 is oriented relative to the coil in the manner already described and it is fixed to the coil by means of a flexible adhesive avoiding any stress or mechanical deformation.

During the operation of the motor, positive and negative pulses are applied successively to the windings 15 and 16, so that these generate a magnetic field whose direction is indicated by the arrow 73 in FIG. 2. The application of each voltage pulse advances the rotor by one step, corresponding to a rotation of 180 °, until it is in the axis of the poles 45, 46, that is ie at an angle a with the normal to the direction of the field indicated by the arrow 73. The rotor stops at this position. The application of io the next pulse turns the rotor again by half a turn, until it is in the axis of poles 45, 46.

The angle a can be of the order of 30 \ which ensures that the rotor always starts in the same direction.

Because the rods 45 and 46 are placed on the annu-15 cylinder head, they are sufficiently distant from the rotating part 12 so that the starting torque required after a stop does not become excessive and does not cause a high energy consumption of the battery during each startup. The service life of the battery is thus extended.

The annular yoke 13 must be of a material with high permeability and low remanence.

The inclination of the bottoms 32, 33, 34 and 35 of the longitudinal grooves makes it possible to use a rotor 19 whose diameter is approximately 25 20% larger than in an engine comprising a coil having roughly the same diameter but whose windings have a rectangular cross section. It thus becomes possible to obtain a higher torque, or greater power on the motor shaft for the same consumption of electrical energy.

The recesses 36 and 37 visible in FIGS. 1 and 6 for mounting the large cheeks 38 and 39 allow precise alignment and positive centering of the rotor shaft relative to the coil constituting the support of the fixed part of the motor. The cheeks simultaneously enclose the rotating part entirely and prevent parts of the windings from protruding into the cavity in which the rotor turns. The tight fit of the cheeks in the recesses also gives the support of the fixed part of the motor a rigidity impossible to achieve by the single molded plastic coil, which prevents the deformation that could cause the pressure exerted by the numerous turns of the windings. .

The blocking of the two cheeks in their recesses by the hot application of a bead of plastic or synthetic material 45 on the cheeks ensures a rigid and undetachable assembly as well as a positive positioning definitively defining the radial clearance and the axial clearance of the rotor relative to the coil. The flanges comprising the bearings and the coil actually become a single rigid part. The bearings forming part of this single piece, constituting the support for the whole of the motor, are spaced apart as much as possible from each other, which allows precise alignment and reduction of the radial deflection of the shaft end. bearing the drive pinion. As can be seen from the drawings, each bearing acts both radially and axially, so that it is not necessary to provide particular thrust bearings. Fig. 3 shows that part of the sleeve 58 comprising the inner rim forming the bearing 59 projects axially from one of the radial faces of the motor; this sleeve part being perfectly concentric with the shaft and its outside diameter being within tight tolerances, it allows the motor to be mounted precisely in the watch movement by simply fitting this sleeve part into a hole provided for this effect in movement.

The ends 64 and 65 of the windings are disposed transversely 65 in the notches 66 and 67 of the ends forming solder lugs 49 and 51 of the connection pins 52 and 53 and are welded thereto. During assembly, the ends of the wires 64 and 65 can be held in place by means of droplets of

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glue 77 and 78 which are removed with the end of the wire which is attached thereto when the welds on the lugs 49 and 51 are completed. The miniature motor according to the invention therefore constitutes a complete and independent unit of the watch, which can be simply plugged into the printed circuit or other organs of the watch in order to ensure the functioning thereof.

Claims (2)

3,631,856 CLAIM 1. Miniature motor for a timepiece movement, comprising a non-magnetic stator having a central cavity of predetermined dimensions, an annular carcass of high permeability and low remanence contiguously surrounding the stator, windings arranged inside the stator to create a magnetic field of determined direction when they are excited by the pulses of control current, a rotor comprising a shaft on which is mounted a permanent magnet having north and south poles, this rotor advancing step by step of 1800 with each excitation windings and being arranged inside the central cavity, this motor being characterized in that the stator comprises a coil body in one piece which has longitudinal and transverse grooves receiving the windings; in that two relatively rigid non-magnetic discs are fixed by their periphery to the internal surface of the stator to close the cylindrical cavity and thus define a chamber and to stiffen the motor assembly; in that these discs each comprise a central support coming in one piece with the disc and extending perpendicularly out of the disc on the side opposite to the cavity, these supports constituting the bearings of the rotor shaft; in that the carcass is cylindrical and is fixed to the coil body, and in that two pole pieces of high permeability and low remanence are fixed on the inside wall of the carcass but outside the windings, these two pieces being distant from the rotor and extending parallel to its shaft so that they establish a magnetic polarization only when one of the poles of the rotor comes close, in order to stop the rotor at a determined position relative to the normal of the field magnetic produced by the windings. 2. Motor according to claim 1, characterized in that the pole pieces each consist of a soft iron rod.