Miniature Motor

Abstract

A miniature electric motor is disclosed wherein a synthetic bobbin or frame has a rotor inside of a central cylindrical cavity, the rotor being supported in bearings which include large diameter flanges bonded to the bobbin. The windings are disposed around the bearing flanges and in grooves whose bottom surfaces are tangential to the cylindrical cavity. The windings thus assist in holding the bearing flanges to the bobbin and form part of the motor framework. The angular bottom surfaces effects increase in the number of turns in the windings and effects an increase in the rotor diameter and thus in the motor torque. A slightly elliptical ring yoke of high permeability and low remanence surrounds and is bonded to the bobbin, the minor axis of the ellipse being at a slight angle to the normal of axis of the field created by the windings to create poles for stopping the rotor at a predetermined position. The major axis of the ellipse is only slightly larger than the minor axis to keep the starting torque requirements low, thereby preventing increase in power consumption.

Description

BACKGROUND OF THE INVENTION

This invention relates to pulse operated miniature electric motors, more particularly to such miniature motors having good starting torque and low power consumption for watch movements and it is an object of the invention to provide improved miniature motors of this nature.

Electric motors for watch movements by their very nature are small devices, usually being of the order of a few millimeters in overall dimensions. Miniature watch motors are known to the art and most, if not all, of them present some problems of ease of assembly, disassembly, efficiency, and torque.

This application provides efficient and simple solutions for these problems and presents a motor which is an integral unit separate from the watch requiring no assembly into the watch movement and no need for wiring. Simply stated, the motor can be plugged into the printed circuit or other operating components of the watch without any separate electrical connections. The motor is positively located in the watch movement and provisions are made for several different methods of securing or mounting it in place.

Accordingly it is a further object of the invention to provide an improved pulse operated miniature electric motor of the nature indicated which is simple to manufacture, easy to assemble into a watch movement, provides positive starting, and accurate stepping of the movement.

It is a further object of the invention to provide a motor of the nature indicated that is inexpensive to make and efficient in operation.

Further objects and advantages will become apparent as the description proceeds.

SUMMARY OF THE INVENTION

In carrying out the invention in one form there is provided a miniature motor for a timepiece comprising: a non-magnetic stator having a central cylindrical cavity of a predetermined diameter and a predetermined longitudinal dimension; two non-magnetic, relatively rigid disk closures attached at their peripheries to said stator for closing said cylindrical cavity to define a chamber and for rigidifying the assembly of said disks and stator; shaft bearings disposed centrally of said disk closures; a shaft disposed in said bearings; a permanent magnet member having a north and a south pole mounted on said shaft interiorly of said chamber; longitudinal and transverse slot means in said stator exteriorly of said cavity and said disk closures, the transverse dimension of said slot means increases as said transverse dimension approaches the diameter of said cavity; winding means disposed in said slot means for providing a magnetic field of a predetermined direction; an elliptical ring yoke of high permeability and low remanence surrounding and attached to said stator for further support thereof; the minor axis of said ellipse being at an angle to the normal of the direction of said field; and the major axis of said ellipse being greater in length than the minor axis of said ellipse to provide bias means for stopping the motor in the same position after each energization of said winding means and for reducing the starting torque following the application of a starting energization.

In carrying out the invention in another form the minor axis of the ellipse is at an angle of 20.degree.-30.degree. to the normal of the field direction and the excess in length of the major axis over the minor axis is about two-three thousandths of an inch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view on an enlarged scale somewhat fragmentary and with a section cut away of a motor according to the invention;

FIG. 2 is an elevational view on a different scale taken substantially in the direction of the arrows 2--2 of FIG. 1;

FIG. 3 is an elevational view taken substantially in the direction of the arrows 3--3 of FIG. 2;

FIG. 4 is a plan view with a cut out portion of one component of the invention;

FIG. 5 is an elevational view taken substantially in the direction of arrows 5--5 of FIG. 1; and

FIG. 6 is a side view with a section broken out taken substantially in the direction of arrows 6--6 of FIG. 5; and

FIG. 7 is a diagrammatic view illustrating certain positions of the components in the functioning circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings the invention is shown as comprising a motor 10 including a stator 11 and a rotor member 12. The stator comprises a ring yoke 13, a winding bobbin or motor frame 14, winding coils 15 and 16 and bearing members 17 and 18. The rotor member 12 comprises a rotor 19 which may be in the form of a disk and a shaft 21 attached to the center of the rotor 19 as by some adhesive, for example an epoxy. The rotating member 19 may be formed of any well known high permeability, high magnetic strength magnetic alloys such for example as samarium cobalt and is magnetized such that north and south magnetic poles exist on opposite ends of a particular diameter. In some instances it may be convenient to use an ordinary bar magnet as compared with a disk member.

The motor frame member or bobbin 14, also shown in FIGS. 4, 5 and 6 comprises a one piece molded construction according to a preferred form of the invention. The material may be nylon, polyvinylchloride or any other synthetic material having sufficient dimensional stability and rigidity for the intended purposes. The material must be non-magnetic and in appropriate instances may also be formed of brass or aluminum, for example, although these metals would have to be annodized to produce an insulating surface so as to not risk short circuiting the windings which are ultimately disposed on the bobbin.

The bobbin 14 is essentially a cylindrical piece having a central cylindrical cavity 22 therein within which the rotor 19 is ultimately received, there being sufficient clearance between the walls of the cavity 22 and the surfaces of the rotor 19 for this purpose. On one side of the center of the bobbin 14 transverse grooves 23 and 24 (FIG. 6) are formed and correspondingly on the other side of the center of the bobbin transverse grooves 25 and 26 are formed. On the one side of the center of the bobbin, longitudinal grooves 27 and 28 are formed and on the other side of the bobbin, longitudinal grooves 29 and 31 are formed. The grooves 23,24 and 26,28 form one winding slot into which the winding 15 is wound or disposed, and the grooves 25,26 and 29,31 form another winding slot into which the winding 16 is wound or disposed.

The inner surfaces or bottoms 68,69 and 71,72 of the grooves 23 and 24, respectively, are parallel to each other as may be seen best in FIG. 6 but the interior surfaces or bottoms of the grooves 27 and 28, as shown for example, by lines 32 and 33 respectively in FIG. 5 are at an angle to each other and are in effect tangent to the cylindrical surface of the cavity 22. The angular disposition of the bottoms 27 and 28 enables more turns of wire to be disposed in the winding groove as compared with a winding groove wherein the bottoms 27 and 28 were parallel to each other. This may be observed in FIG. 2 by noting the darker cross hatched portion 20 as compared with lighter cross hatched portion 30.

In addition the angular bottoms 27 and 28 enable the winding disposed in the grooves to be closer to the cylindrical wall of cavity 22 and thus closer to the surface of the magnetic rotor 19 which will be disposed therein. A more efficient magnetic circuit is thereby achieved. The motor is enabled to develop a higher torque level or more power output for the same power input. Similarly the grooves 29 and 31 have angularly disposed bottom surfaces as shown by the lines 34 and 35, respectively, and the winding groove formed by the slots 25,26 and 29,31 will receive more turns for the same stated reasons. The angular bottom surfaces 27,28 34, and 35 enable about 20% more turns to be disposed in the winding grooves as compared with ordinary constructions.

The end of the cylindrical cavity 22 terminates in circular grooves 36 and 37 which are adapted to receive, respectively, the flanges 38 and 39 of the bearing members 17 and 18, as will be more particularly described.

Theformation of the winding grooves 23,24 and 27,28 and 25,26 and 29,31 leaves two segment-shaped portions 41 and 42 and to radial boss-like members 43 and 44. Longitudinal grooves 45 are disposed in the outer periphery of the segment-like members 41 and 42 and longitudinal grooves 46 are disposed in the outer peripheries of the boss-like members 43 and 44. The grooves 45 and 46 are utilized for cementing or bonding the bobbin to the ring yoke 13 as will be described. Radial grooves 47 and 48 are formed, as shown, in the segment portions 41 and 42 to receive the ends 49 and 51 of connecting pins 52 and 53. The enlarged ends 49 and 51 of the connecting pins 52 and 53 are press fitted into holes 54 and 55 in the segment members 41 and 42 respectively. Holes 56 and 57 are formed, respectively, in the boss-like members 43 and 44 for receiving attaching screws in the event that such be desired.

The bearing member 17 includes a sleeve portion 58 and a large diameter radially extending flange 38 at right angles thereto at one end. At the other end a smaller flange 59 exists which includes the actual bearing surface centrally thereof for receiving one end of the shaft 21. Similarly the bearing member 18 includes a large diameter radially extending flange 39 projecting at right angles to a sleeve portion 60. At the other end a second and smaller diameter flange 61 exists at the inner central area of which there is the actual bearing surface for holding the other end of shaft 21. By having the bearing flanges 59 and 61 placed at the ends of the sleeve portions 58 and 60 the bearing surfaces for the shaft 21 are disposed far apart so that the shaft 21 is supported in a very stable and accurate manner. The bearing members 17 and 18 may be formed of any suitably hard non-magnetic and dimensionally stable material. One type of such material which has been found to be satisfactory is the alloy beryllium copper. The bearing flanges 59 and 61 made of beryllium copper may run without lubrication as is well understood although lubrication of course may be provided.

In the assembling process the rotor 19 may be first assembled to the shaft 21. Thereafter the rotor and shaft are disposed in the cavity 22 of the bobbin or frame 14. This is followed by disposing the flanges 59 and 61 of the bearing members 17 and 18 over the appropriate ends of the shaft 21 and the outer peripheries of the large diameter flanges 38 and 39 in the respective grooves 36 and 37 at the ends of the cavity 22. While in this position beads 62 of synthetic material which may be of the same nature as that of the bobbin itself are formed over the outer peripheries of the flange members 38 and 39 as by the application of a heated tool. Beads 62 are formed in association with the surfaces of the grooves formed inwardly of the segmentshaped members 41 and 42 as may be seen best in FIG. 1. The flange members 38 and 39 are thus firmly bonded to the bobbin 14 and form therewith a relatively rigid structure which accurately and firmly holds the shaft 21 in the proper position.

After the bobbin 14, the rotor 19 and shaft 21 together with the bearing members 17 and 18 have been assembled together, the windings 15 and 16 are wound in the appropriate grooves. The windings, or coils, 15 and 16 are wound in the grooves described along the angular surfaces 32, 33, 34 and 35 under ordinary tension for wire of the size as used here which for example may be No. 55 ASW. 156 feet in total comprising about 2,200 turns in each of coils 15 and 16 are wound as described and the resistance of the windings may be about 5.6K ohms. The winding tension results in the inner surface of the cylindrical cavity 22 firmly engaging the outer edges of the bearing flanges 38 and 39 thereby forming a relatively rigid and in effect a monolithic structure. The windings being disposed on the outside of the bearing flanges 38 and 39 thus provides a significant portion of the strength of the unit. Referring to FIG. 2 it will be seen that the coils 15 and 16 are connected by a run 63 of wire and the ends 64 and 65 of the coils are disposed across and in the grooves 66 and 67 in the ends 49 and 51 of the connecting pins 52 and 53.

The grooves 36 and 37 (FIG. 6) terminating the end of the cylindrical cavity 22 are disposed inwardly of the surfaces 68 and 69, 71 and 72, which form the inward surfaces of the grooves receiving the windings. Accordingly it will be evident that the innermost layer of the windings 15 and 16 are disposed slightly away from the surfaces of the bearing flanges 38 and 39 thereby avoiding the possibility of short circuits.

Surrounding the assembly of the rotor, bobbin and windings is the ring yoke 13. The ring yoke is in the form of a shell or annulus having a longitudinal, or axial, dimension equal to or slightly greater than the longitudinal dimension of the bobbin 14. The inner diameter of the ring 11 is just slightly larger than the diameter of the bobbin 14 so that the ring may be received thereover in very close fitting relationship. The slots 45 and 46 in the outer periphery of the bobbin 13 are utilized to receive a cement such as for example as an epoxy for tightly cementing the ring yoke 11 to the bobbin 14. Thereby additional rigidity and strength are imparted to the motor as a whole.

The ring yoke 11 is not a precise circle but differs therefrom slightly and actually is in the form of an ellipse. Reference is made to FIGS. 2 and 7 in this connection. In FIG. 2 the actual dimensions of one specific form of motor are shown. In this Figure the major axis of the ellipse is shown to be 0.2474 inches while the minor axis is shown to be 0.2444 inches. In other words the minor axis is about three thousandths of an inch less than the major axis. In the actual case it was found that the minor axis of the ellipse should be between two thousandths and three thousandths of an inch less than the major axis. The elliptical shape of the ring yoke 13 provides for poles at the ends of the minor axis as may be seen in FIG. 7, and determines the stationary position of the rotor 12. During operation, positive and negative pulses in succession are applied to the windings 15 and 16 and provide a magnetic field in the direction of the arrow 73 in FIG. 7. The application of each voltage pulse causes the rotor to step, rotate so to speak, 180 degrees thereby coming opposite the poles determined by the minor axis of the ellipse. The rotor becomes stationary at this point. The application of the next pulse again causes the rotor to step one-half of a revolution, and again it comes to rest at the poles determined by the minor axis of the ellipse.

The difference between the major and minor axes of the ellipse is small in order to create, on the one hand, poles so that the rotor comes to rest at the same point after each energization. On the other hand the difference cannot be too great, or the power required to break the rotor loose for the next succeeding half revolution becomes too large. Appropriate choice of the difference keeps the power consumed by the motor. The elliptical cross section is required to provide poles for stopping the rotor and the difference in dimensions must be smaller in order to prevent excessive torque being required.

The major axes 75 of the ellipse is disposed at an angle shown clockwise in FIG. 7 with respect to the axis 73 of the field created by the windings. The minor axis 74 on which the north and south poles of the ring yoke 13 lie is therefore at the same angle to the normal 76 to the direction of field 73. In this manner the rotor 12 stops with its north-south axis always at a slight angle to the normal 76 of the direction of field 73 and enables the starting torque to be applied to the same direction at each application of a positive or negative pulse. Accordingly the motor always runs in the same direction. The angle .alpha. between the minor axis 74 and the normal 76 is in the vicinity of 20.degree.-25.degree. in the practical case described.

The ring yoke 13 should be of any high permeability low remanence material such as that available under the trade name of Hypernic.

Because the inner surfaces 32,33,34 and 35 of the winding grooves are at an angle, the rotor 19 may be approximately 20 percent larger in diameter than is possible in constructions where the coil shape is parallel sided and of comparable diameter. Higher torque level, or more power output, for the same electrical input is achieved.

The recesses 36 and 37 illustrated in FIGS. 1 and 6 provide mounting space for the wide flange bearing 38 and 39, allowing for extremely accurate alignment and positive centering of the rotor shaft to the motor frame. The bearing flanges also serve the purpose of entirely enclosing the rotating parts and preventing the wire winding from protruding into the rotor cavity. Also, being a close fit in their respective seats they impart a rigidity to the motor frame impossible to achieve with the molded plastic bobbin itself, thus preventing distortion due to the pressure of the many turns of tension wire wound on it.

The method of locking the two bearing flanges in place by hot pressing a bead of plastic or synthetic material over them provides a rigid mounting and positive end play positioning without any possibility of coming loose or loosening alignment. The bearings and frame become, in effect, one solid piece. The bearing surfaces themselves are an integral part of the whole bearing assembly and are spaced as far apart as possible for positive alignment and reduction of radial movement at the pinion end. Each bearing, as may be seen, is both radial and thrust, thereby eliminating the need for additional thrust bearings. The bearing 59 extends beyond the plane of the base of the motor as may be seen in FIG. 3, and its outside diameter is held to very tight concentricity and size tolerances. This provides a boss by which the motor can be accurately located in the watch movement by simply inserting the boss into a properly located hole in the watch movement.

The ends of the windings 64 and 65 are disposed across the grooves 66 and 67 in the end lugs 49 and 51 of the connecting pins 52 and 53. A blob of solder may be disposed over the winding in the grooves 66 and 67 for firmly holding the ends of the coils in place. During assembly the ends of the wires 64 and 65 may be held as shown with a dab of cement 77 and 78 until the actual soldering operation is performed whereafter the blob of cement and the attached wire end are removed.

It has been found that the ring yoke 13 need not have any apertures or perturbations for creating any bias, or poles, for holding the position of the rotor but this effect is achieved by having a solid ring as shown but in elliptical form rather than circular.

In one particular form of watch motor the diameter of the cavity 22 was 0.128 inches. the longitudinal dimension of the cavity 22 between flanges 38 and 39 was 0.040 inches, and the diameter of the rotor 12 was 0.117 inches. The diameter of the flanges 38 and 39 was 0.1365 inches and the thickness of the flanges was 0.0055 inches. It will be understood of course that small tolerances are available in each of these dimensions as will be clear to those skilled in the art. Other dimensions of course may be used for particular constructions of motors to meet the particular conditions.

Claims

1. A miniature motor for a timepiece comprising:

A non-magnetic stator having a central cylindrical cavity of a predetermined diameter and a predetermined longitudinal dimension;

two non-magnetic, relatively rigid disk closures attached at their peripheries to said stator interiorly of its periphery for closing said cylindrical cavity to define a chamber and for rigidifying the assembly of said disks and stator;

shaft bearing supports integral with and disposed centrally of said disk closures;

said bearing supports projecting perpendicularly to said disk closures;

Shaft bearing disposed at the ends of said shaft bearing supports;

a shaft disposed in said bearings;

a permanent magnet member having a north and a south pole mounted on said shaft interiorly of said chamber;

longitudinal and transverse slot means in said stator exterior of said cavity and said disk closures, the transverse dimension of said slot means increasing as said transverse dimension approaches the diameter of said cavity;

winding means disposed in said slot means for providing a magnetic field of a predetermined direction;

an elliptical ring yoke of high permeability and low remanence surrounding, and attached to, said stator for further support thereof;

the minor axis of said ellipse being at an angle to the normal of the direction of said field; and

the major axis of said ellipse being greater in length than the minor axis of said ellipse to provide bias means for stopping the rotor in the same position after each energization of said winding means and for reducing the starting torque following the application of a starting energization.

2. A miniature motor according to claim 1 wherein the minor axis of said

3. A miniature motor according to claim 1 wherein the excess in length of said major axis over said minor axis is about two to three thousandths of

4. A miniature motor according to claim 1 wherein said slot means comprises

5. A miniature motor according to claim 4 wherein the interior surface of said windings is disposed away from the surfaces of said disk closures.

6. A miniature motor according to claim 1 wherein each of said closure disks includes a longitudinal sleeve along the bearing axis of said shaft

7. A miniature motor according to claim 1 wherein said stator includes a pair of longitudinal openings beyond the periphery of the disk closures, and includes contact members disposed in said openings.