GB2091496A

GB2091496A - A Stepping Motor

Info

Publication number: GB2091496A
Application number: GB8138084A
Authority: GB
Original assignee: ELEKTROMASCH FORSCH ENTWICK
Current assignee: ELEKTROMASCH FORSCH ENTWICK
Priority date: 1980-12-23
Filing date: 1981-12-17
Publication date: 1982-07-28
Also published as: GB2091496B; DD155747A1; DE3143923A1; NL8104999A; JPS57126266A

Abstract

In a homopolar permanently- excited single-stator stepping motor, the rotor is formed, in the axial direction, by at least two annular magnets 8 which are separated, in each case by grooved flux-conductor discs 6. The magnets 8 are arranged with their poles in opposition, the adjacent flux conductor discs 6 being in each case displaced with respect to one another by half the groove- spacing. The discs 6 have a diameter/length ratio of at least 2.5:1. The arrangement reduces eddy current losses and allows magnets of low residual induction to be used. The invention can be used in the field of electrical machinery construction, as well as for special drive-mechanisms for use in electronic data-processing. <IMAGE>

Description

SPECIFICATION A Stepping Motor The present invention relates in particular to a homopolar permanently-excited single-stator stepping motor, which is particularly suitable for the use of permanent magnets having low residual induction values.

Stepping motors with homopolar magnetised rotors have the advantage compared to other stepping motors that it is possible to generate very small stepping angles, and to reproduce these angles, even in designs having small numbers of poles. A disadvantageous effect occurring in these stepping motors is that the magnetic flux in the stator always exhibits an axial component, for reasons deriving from the design principle.

This axial component of the magnetic flux is opposed by high magnetic resistance, created by the laminated construction of the stator body, this high resistance reducing the magnetic flux. At the same time, the magnetic flux, running perpendicularly to the plane of the laminations, gives rise to eddy currents, which lead to losses and to degradation of the dynamic characteristics of the stepping motor.

Various proposals for reducing these disadvantages have already been put forward.

Thus, the use of permanent magnets having high residual induction values, for example AlNiCo magnets, has been disclosed in German Auslegeschrift 2,703,791, since such magnets enable a sufficiently high magnetic field to be obtained in the stator, despite the high magnetic resistance. This solution has the disadvantage that the eddy currents and the consequential disadvantageous influence on the losses and the dynamic characteristics continue to exist.

It is known, according to U.S. Patent Specification 2,931,929, and also according to German Offenlegungsschrift 1,488,691 to reduce the magnetic resistance of the stator by means of a steel housing, which conducts to the axial flux.

This measure admittedly enables magnetic materials having low residual induction values to be employed, but the eddy-current losses and their disadvantageous effect on the dynamic characterisics of the motor remain unaffected, even after this design solution has been applied.

It is a general object of the present invention to reduce the losses in homopolar permanentlyexcited single-stator stepping motors, and to improve their dynamic characteristics.

According to one aspect of the present invention there is provided an arrangement for the magnetic circuit, whereby the formation of eddy currents in the stator is suppressed to the greatest possible extent.

In particular, the present invention provides homopolar permanently-excited single-stator stepping motor, having a stator which consists of a laminated magnet body, with salient poles carrying the operating windings, and having a rotor which consists of an axially magnetised annular magnet and grooved flux conductor discs, which are connected to the poles at the periphery, these discs being mutually displaced by half the groove-spacing, characterised in that the rotor possesses at least two annular magnets in the axial direction, over a length equal to that of the stator, these magnets being arranged with their poles in opposition and being separated, in each case, by flux-conductor discs, and having a diameter/length ratio of at least 2.5:1, and their flux-conductor discs being alternately displaced with respect to one another by half the groove spacing.

In an advantageous further development, the annular magnets, which alternate in the axial direction, with the flux conductor discs are designed to have a diameter/iength ratio of 10:1.

If the diameter/length ratio is chosen to be between 2.5:1 and approximately 6:1, it is expedient, with regard to the flux distribution in the air gap, to design the flux-conductor discs to be wider at the periphery than in the region corresponding to the diameter of the annular magnets.

The rotor design according to the invention, ensures that the flux in the stator passes smoothly from lamination to lamination and that surprisingly the eddy currents which are caused by axial components of the magnetic flux, are thereby reduced to a significant extent. As a consequence of this reduction in the eddy currents the losses are significantly lowered, and the dynamic characteristics of the stepping motor are considerably improved.

The effect according to the invention increases as the diameter/length ratio of the annular magnets increases, this increase, however, necessitating the parallel connection of several annular magnets in order to obtain an adequate torque, the magnets being separated by fluxconductor discs.

The technological effect, resulting from this, sets an economic limit to the application of the invention.

The solution according to the invention particularly favours the use of inexpensive permanent magnet materials, such as, for example, hard ferrites.

Reference is now made to the sole accompanying drawing which illustrates a longitudinal section through a homopolar permanently-excited stepping motor, designed in accordance with the invention.

As is usual in electrical machines, the stator 1 is of laminated design, and possesses salient poles 2, which carry the operating winding 3. The surface of the poles 2 facing the air gap 4 can be furnished with a series of grooves, depending on the stepping angle which is to be achieved.

Fourflux-conductordiscs 6 are located as load-bearing bodies, on a non-magnetic shaft 5, these discs possessing a series of grooves 7 on their periphery. The series of grooves 7 is displaced by half a groove-spacing at adjacent flux conductor discs 6.

Three axially magnetic annular magnets 8 are located between the flux conductor discs 6. These magnets are centered by shoulders 9 on the outer periphery of the flux-conductor discs 6. The mutually opposing surfaces of the annular magnets 8 have the same polarity, so that an alternating sequence of poles always occurs in the axial direction.

An anisotropic hard ferrite, having an axial preferred direction, is employed as the material for the annular magnets.

Claims

1. Homopolar permanently-excited singlestator stepping motor, having a stator which consists of a laminated magnet body, with salient poles carrying the operating windings, and having a rotor which consists of an axially magnetised annular magnet and grooved flux conductor discs, which are connected to the poles at the periphery, these discs being mutually displaced by half the groove-spacing, characterised in that the rotor possesses at least two annular magnets in the axial direction, over a length equal to that of the stator, these magnets being arranged with their poles in opposition and being separated, in each case, by flux-conductor discs, and having a diameter/length ratio of at least 2.5:1, and their flux-conductor discs being alternately displaced with respect to one another by half the groove spacing.

2. A stepping motor according to Claim 1 characterised in that the annular magnets have a diameter/length ratio of 10:1.

3. A stepping motor according to Claim 1 characterised in that, for a diameter/length ratio of 2.5-6, the flux conductor discs are designed to be wider at the periphery than in the region corresponding to the diameter of the annular magnets.

4. A stepping motor according to Claim 1 substantially as described with reference to and as illustrated in the accompanying drawing.