GB2032705A - Axial air-gap electric motors: mounting rotors - Google Patents

Abstract

A stepping motor comprises a disc-shaped rotor (1) mounted on an axle (2), and two polar stator parts (5a, 5b) placed in axially facing relationship to form an axial air gap; the polar parts each have an opening (5) to allow insertion of the rotor into its operating position after assembly of the stationary magnetic circuit by relative movement between the rotor and the stator in a direction perpendicular to the axis of the rotor. The motor may be used in a timepiece. <IMAGE>

Description

SPECIFICATION Electrical stepping motor The present invention relates to electrical stepping motors, and more particularly to stepping motors comprising a disc-shaped, axially magnetized rotor part mounted for rotation in the air gap of a stator structure. The stator structure of the type of motors concerned by the invention includes two polar parts placed in axially facing relationship to form said air gap, said polar parts being coupled to an electrical coil. Current pulses are supplied to said coil for driving to rotor from one stable position to the next one.

Motors of this type are described in Swiss patent 599707.

In some fields of use of electrical stepping motors, such as in electric watches, recent developments have lead to structures in which the motor is integrated in the whole mechanical device, i.e. the watch movement, rather than mounted in that device as a separate component. As a separate component the motor was completely finished, closed and checked by its manufacturer and could be replaced as an independent part of the device.

The stepping motor according to the invention comprises an axially magnetized discshaped rotor part mounted on an axis, and a stationary magnetic circuit including two polar parts forming an air gap in which said rotor part is arranged for rotation and an electrical excitation coil coupled to said polar parts. The polar parts are arranged in axially facing relationship to form said air gap and have an opening the shape of which is adapted to allow lateral introduction of the rotor axis, so that the said rotor part mounted on its axis can be placed in its operating position in the air gap after assembly of the stationary magnetic circuit by shifting the said magnetic circuit in a direction perpendicular to the rotor axis.

By the design according to the invention the motor can be manufactured in two separate parts and the assembly or dismounting thereof is an easy, quick operation which does not affect the magnetic properties of the circuit. This design therefore allows to combine the advantages of a completely finished and tested individual motor with the advantages of a motor which can be mounted as an integral part of the device in which the motor is used.

The invention will be better understandable by the following description of a preferred embodient thereof when read in conjunction with the accompanying drawing. In that drawing Figure 1 is a lateral view of a multipolar stepping motor according to the invention and Figure 2 is a top view of the motor of Fig.

1.

The stepping motor shown in Figs. 1 and 2 comprises a disc-shaped rotor part 1 mounted on an axis 2. The disc 1 is magnetized in an axial direction so as to present a plurality of pairs of magnetic poles on each of its faces, positive and negative poles being formed alternately in the direction of rotation. In the present example six pairs of poles appear on each face of the rotor disc.

Axis 2 is adapted to be supported in bearings 3 and 4 represented schematically in Fig.

1. These bearings are part of the device in which the motor is to be incorporated, for instance a watch movement.

The stator structure of the motor comprises two polar parts 5a and 5b of identical shape, having each a plurality of teeth designated by 5a' and 5b', respectively.

One of the teeth of each polar part is connected through a respective supporting arm 5a", 5b" to a respective core part 5a"', 5b"', which core parts are superposed along the axis of a cylindrical excitation coil 6 to form the core thereof.

For assembling the stator structure of the present example, it is sufficient to introduce the core parts 5a"', 5b"' into the central hollow part of coil 6 which coil is wound on a coil support having flanges 7 and 8, the coil support being adapted to maintain the parts 5a"' and 5b"' in superposed relationship. In particular, each of the flanges 7 and 8 can be provided with a respective lateral groove 7', 8' to maintain the supporting arms 5a" and 5b", groove 7' being disposed in the upper half of flange 7, as shown in Fig. 1, and groove 8' extending similarly in the lower half of flange 8.As further shown in Fig. 1, the arms 5a" and 5b" have a bent configuration to support the teeth 5a' and 5b' of the respective polar parts on either side of rotor disc 1.

To increase the stability of the stator structure, besides supporting arms 5a" and 5b" connected to a first pair of teeth 5a', 5b', additional supporting arms 5aiV and 5biV are provided in connection with a second pair of teeth 5a', 5b', the ends of these additional supporting arms being inserted in corresponding openings 7" and 8" of coil flanges 7 and 8.

As shown in Fig. 2, the teeth 5a' and 5b' of polar parts 5a, 5b are connected to each other and supported by central parts 5a" and 5b", respectively. These central parts define an opening 5 of the stator structure, the dimension and shape of said opening allowing the rotor axis 2 to be placed in its operating position with respect to the magnetic circuit constituted by the stator structure of the motor.

It will be seen from the drawing that the two polar parts 5a, 5b together with their supporting arms and respective core parts are formed by pieces of identical shape turned with respect to each other by 180 and super posed along the contact surface of the core parts 5a"', 5b"'. The manufacturing and assembling operations can therefore be considerably simplified and substantial cost reduction achieved. Moreover, the superposition of the said core parts along the whole length of the coil allows to reach an excellent magnetic joint between these parts.

The stator structure as described above can be manufactured as a complete, separate module which is associated to the rotor part of the motor only at the time of assembling the mechanical device to be driven.

The rotor part can therefore be mounted independently of the stator structure as an integral part of the said mechanical device and the stator structure can be placed and fixed in this device separately. More particularly, in the present example, the stator structure can be positioned by shifting the same laterally, i.e. perpendicularly with respect to the rotor axis, into its operating position.

An important advantage of the present invention is the fact that the stationary magnetic circuit of the motor can be completely assembled and checked with respect to its magnetic properties before the assembling of the motor and can be replaced or dismounted and remounted, for instance for lubrication of the rotating parts, as an independent module.

This allows to achieve very high and equal performances of the motors when manufactured in great series as well as to reduce the manufacturing costs of the whole device in which the motor is used.

Claims (4)

1. An electrical stepping motor comprising an axially magnetized disc-shaped rotor part mounted on an axis, and a stationary magnetic circuit including two polar parts defining an air gap in which said rotor part is capable of rotating and an electrical excitation coil coupled to said polar parts, said polar parts being arranged in axially facing relationship to form said air gap and having an opening the shape and the dimension of which are adapted to allow the said rotor part mounted on its axis to be placed in its operating position in the air gap after assembly of the stationary magnetic circuit by shifting the said magnetic circuit in a direction perpendicular to the rotor axis.

2. A multi polar electric stepping motor comprising an axially magnetized disc-shaped rotor part mounted on an axis, a stationary magnetic circuit including two polar parts in axially facing relationship to form an air gap in which the said rotor part is arranged for rotation, and a cylindrical electric excitation coil coupled to said polar parts, said discshaped rotor part presenting on each face thereof, in circumferential direction, a plurality of alternately positive and negative magnetic poles and said polar parts having each a plurality of cut-out teeth in axially facing relationship, the teeth of each polar part being arranged in a same plane and connected to each other by a central connecting part, at least one tooth of each part extending beyond its outer peripheral part to form a supporting arm including an elongated end part the said polar parts being placed in contact with each other at least over the greater part of the length thereof and forming at least a part of a core of the said coil, the said polar parts and the excitation coil forming a stator structure independant of the rotor, said central connecting part having an opening on its side opposite to that of the excitation coil, the shape and dimension of said opening being adapted to allow lateral introduction of the rotor axis, so that the said rotor part mounted on its axis can be placed in the air gap between the polar parts in its operating position after complete assembly of the stator structure by shifting the said magnetic circuit in a direction perpendicular to the rotor axis.

3. A multipolar stepping motor as claimed in claim 2, wherein the said polar parts are of identical shape and are placed symmetrically with respect to the plane of the rotor disc.

4. A multipolar stepping motor substantially as hereinbefore described with reference to the accompanying drawings.