GB2188790A

GB2188790A - Switched stator winding for an electric motor

Info

Publication number: GB2188790A
Application number: GB08608220A
Authority: GB
Inventors: David Barrie Hawthorne; Roman Derc
Original assignee: Data Recording Instrument Co Ltd
Current assignee: Data Recording Instrument Co Ltd
Priority date: 1986-04-04
Filing date: 1986-04-04
Publication date: 1987-10-07
Also published as: GB8608220D0; GB8630122D0; GB2188791A

Abstract

An improved motor design is disclosed wherein a magnetic soft ring material 10 has a continuous winding 16 wound therearound, with a facility to introduce current into the winding 16 from selected tap points e.g. A and B. A magnet 12 is mounted for rotation at the centre 14 thereof. Alternatively, Fig. 4, a plurality of coils 70, 72, 74, 76 are placed around a magnetic soft ring material, with opposite coils 70, 72 and 74, 76 on the ring material connected in series in a sense such that the series connected coils produce magnetic flux in opposite directions. Appropriate switching of connection and polarity of either pairs A, B or C D in Fig. 1 or appropriate switching of polarity of both pairs E, F and G H, in Fig. 4 produces a continuous rotation of magnet 12. <IMAGE>

Description

SPECIFICATION Improved motor design BA CKGROUND This invention relates to an improved design for an electric motor, and in particular to an improved design for an electrically driven motor which can be used in computer peripherals, such as disc drives, for accurate positioning of magnetic transducer assemblies on magnetic disc.

A magnetic disc provides for the storage of information across the surface thereof in concentric bands known as tracks. Information may be stored thereon and/or extracted therefrom through an associated magnetic transducer which is positionable across the surface thereof over selected tracks thereon.

In the past, the positioning of magnetic transducer assemblies on magnetic disc was typically performed through the use of a stepper motor. A stepper motor, responsive to excitation, produces angular displacement in discrete steps. The stepper motor is typically coupled to the magnetic transducer in such a fashion that rotation of a shaft associated with the stepper motor results in motion of the magnetic transducer across the surface of the magnetic disc.

With demands to store greater amounts of information on the surface of discs, it became necessary to decrease the distance between the tracks thereon. As the minimum displacement producable by a stepper motor is a single discrete step, the size of the step became a limiting factor in the spacing between tracks. This has led, in turn, to requirements that stepper motors produce displacements in increasingly smaller steps.

The electromechanical nature of stepper motors, however, has placed practical limitations on the size of small angular displacements which may be reliably produced. Consequently, alternate devices for the positioning of magnetic transducers have been sought.

Linear voice coil motors have been employed as positioning devices for magnetic transducer assemblies. However, while such motors are free of the electromechanicai limitations of stepper motors, and do offer a significant increase in the speed with which a magnetic transducer assembly may be positioned with respect to a magnetic disk, economic considerations have operated to limit their application.

In an alternate approach, rotary, constant torque motors have been employed. Such motor designs have typically included a ring of soft magnetic material, with an electrically conductive wire wound therearound, collectively referred to as a stator. Inside of the stator and positioned at the center thereof is a permanent magnet assembly, mounted for rotation about the center point of the stator. The permanent magnet assembly is referred to as the rotor.

Magnetic flux is generated by the permanent magnet assembly. In response to an electric current passing through the winding, a force is developed between the stator and the rotor. As the winding is fixed to the ring, the resulting force operates between the rotor and the ring. The force is at right angles to both the flux and the current directions. As the current direction in the gaps at the opposite ends of the rotor assembly is reversed, the forces produced will be in opposite directions, giving the rotor assembly a rotational moment proportional to the rotor radius and the sum of the forces.

While such motors may be manufactured in any of a wide variety of ways, a typical manner is to have the soft magnetic material configured as a toroid, with electrical taps on the winding positioned at opposite sides of the toroid, i.e., 180 degrees apart. With such a winding, the rotation of the rotor would only continue until the center of the rotor poles coincide with the taps. This results from the fact that the current divides at these points in opposite directions, thus producing forces also of opposite directions.

In the past, a second winding has been necessary to provide for continuous rotation. In particular, a second winding is wound about the soft magnetic material over the first winding, with the associated taps being displaced ninety winding, with the associated taps being displaced ninety degrees from the taps associated with the first winding. In such configuration, if the current is switched to the next tap on an alternate winding, and displaced ninety degrees every time a rotor pole approaches a present tap, continuous rotation of the rotor is obtained.

The torque of the foregoing described motor can be made constant if the rotor poles never overlap the current injection points, i.e., the rotor poles must span less than ninety degrees minus the commutation (or current switching) accuracy.

While such a motor design has been found effective in producing the desired rotational displacement, several shortcomings are nevertheless present with such a design. In particular, a second winding is necessary to achieve continuous rotation. According to the foregoing discussed principles of operation, current is only passed through one of the two windings at any one time. Consequently, each of the two windings is only used fifty per cent of the time.

In addition, the current necessary to produce the desired rotation motion must alternately be passed through both windings, requiring either separate drive electronics for both windings, each capable of supplying the full amount of the required current, or a switching arrangement to switch the drive electronics between the two windings. Such a configuration is somewhat inefficient, expensive and unreliable.

Consequently, effeciency, reliability and cost considerations with respect to currently available rotary motors have created a need for an improved motor.

SUMMARY In accordance with the present invention, an improved motor design is disclosed. In one embodiment, a single continuous winding is employed about the magnetic soft permeable material, with taps being made thereon at equally spaced intervals for the introduction of current into the winding. A magnet is pivoted for rotation at the center thereof. Rotation of the magnet is effected by introducing a current into the winding through associated taps. In particular, introducing current into the winding results in the production of a force in those parts of the winding which are situated in the path of the magnetic flux generated between both ends of the magnet and the soft magnetic material ring.This force, which is proportional to the effective length of the wire in the flux field, the magnitude of the current and the magnetic flux density acts between the wire and- the rotationally pivoted magnet causing its rotation. By proper choice of the points about the winding through which the current is introduced, continuous rotation of the magnet in either direction may be achieved.

By using a single continuous winding, only one-half of the total number of windings previously required by designs employing two separate windings is required. Consequently, the same torque may be produced by using only one-half of the number of windings previously required.

Alternatively, by using the same number of windings, twice the torque previously available from designs employing two separate windings is available.

In an alternate embodiment, four identical windings are employed, each occupying one of the four quadrants of a motor core. Two effective windings are formed therefrom by connecting in series windings in opposite quadrants, in a sense such that the magnetic flux produced by one winding will be in opposition to that produced by the opposite winding. By selectively controlling the direction in which current is introduced into the two windings, correct current flow pattern can be maintained with respect to the magnet poles thus providing for the continuous rotation of the rotor in either direction.By using four identical windings as above described, only one-half of the current necessary in the previously discussed embodiment is required for each of the effective windings, thereby providing a significant reduction of the current driving requirements of associated electronic driving circuits.

DESCRIPTION OF THE FIGURES Figure 1 is a functional illustration of one embodiment of the present invention.

Figures 2A and 2B are illustrations of a portion of the apparatus of Fig. 1.

Figures 3A, 3B, 3C and 3D are illustrations of current flow and resulting magnetic flux directions due to these currents in the apparatus of Figs. 2A and 2B.

Figure 4 is a functional illustration of the preferred embodiment of the present invention.

Figures 5A, 5B 5C and 5D are illustrations of current flow and resulting magnetic flux directions due to these currents in the apparatus of Fig. 4.

DETAILED DESCRIPTION Fig. 1 functionally illustrates an improved motor in accordance with the present invention.

Referring to Fig. 1, a circular toroidal ring material 10 of soft magnetic material has positioned in the center thereof a permanent magnet 12, pivoted for rotation about a center point 14. Affixed to permanent magnet 12 at center point 14 is a shaft (not illustrated). Wire 16 is wound about toroidal ring material 10 to form a closed circuit in a continuous winding therearound. Taps A 16, B 18, C 20 and D 22 are connected to the wire wound around toroidal ring material 10 at 90 degree intervals, respectively.

In a preferred implementation of the motor illustrated in Fig. 1, toroidal ring material 10 has a 30mm mean diameter, and is composed of mild steel. The winding around circular toroidal ring material 10 was implemented with a total of 1000 turns of 37 SWG insulated copper wire, wound in 3 layers. The windings, tapped at 90 degree intervals around the coil, produce four equal segments of 250 turns each. The rotor magnet material is either neodynium or samarium cobalt.

The motor described in Fig. 1 operates in the following manner. Current is only supplied at any given time to one set of taps displaced by 180 degrees, i.e., either to taps A 16 and B 18, or taps C 20 and D22. This creates the effect of having two separate coils displaced by 90 degrees, as functionally illustrated in Figs. 2A and 2B. Figs. 2A and 2B are similar to Fig. 1, and like elements have been given corresponding reference designators. For the purposes of clarity magnet 12 is not illustrated in Figs. 2A and 2B. Referring first to Fig. 2A, if current is introduced into winding 16 in a direction from terminal A 16 to terminal B 18, the current will split at the point of connection to the winding, with a first current flowing through a first half 30 of winding, and a second current flowing through a second half 32 of the winding.

Referring now to Fig. 2B, in a similar manner, if current is introduced into winding 16 in a direction from terminal C 20 to terminal D 22, the current will split at the point of connection to the winding, with a first current flowing through a first half 50 of winding 16, and a second current flowing through the second half 52 of winding 16.

As wire 16 is wound in a single direction around toroidal ring material 10, the first and second currents previously discussed with respect to Figs. 2A and 2B will flow in opposite directions around toroidal ring material 10. The direction of current flow with respect to terminals A 16, B 18, C 20 and p 22 is functionally illustrated in Figs. 3A through 3D. Figs. 3A through 3D are similar to Figs. 1, 2A and 2B, and like elements have been given corresponding reference designators. For the purpose of clarity, however, magnet 12 is not illustrated.

Referring now to Fig. 3A, a current flowing in a direction from terminal A 16 to terminal B 18 will divide between the two respective windings, i.e., a first portion of the current flow through a first half 30 of the winding, and a second portion of the current will flow through a second half 32 of the winding. The current which flows through the first half 30 of the winding has a current direction out of the plane of the toroid 10, at its inner radius. The current which flows through the second half 32 of the winding has a current direction into the plane of the toroid 10 at its inner radius. These two current directions are in opposite directions.

When a magnetic rotor (not shown) is positioned inside the toroid such that its opposite poles are straddling the two halves of the coil, through which current is flowing in opposite directions, forces are produced at both ends of the magnet that cooperatively act to produce rotational motion. This rotational motion is limited such that the current injection points are not crossed.

If the direction of the current is reversed the direction of the motion of the rotor will likewise be reversed, referring to Fig. 3B, a current flowing in a direction from terminal B 18 to terminal A 16 will divide between the two respective windings, i.e., a first portion of the current will flow through a first half 30 of the winding, and a second portion of the current will flow through a second half 32 of the winding. The current which flows through the first half 30 of the winding has a current direction into the plane of the toroid, at its inner radius. The current which flows through the second half 32 of the winding has a current direction out of the plane of the toroid 10, at its inner radius. These two current directions are in opposite directions.

When a magnetic rotor (not shown) is positioned inside the toroid such that its opposite poles are straddling the two halves of the coil, through which current is flowing in opposite directions, forces are produced at both ends of the magnet that cooperatively act to produce rotational motion. The rotational motion is limited such that the current injection points are not crossed.

Referring now to Fig. 3C, a current flowing in the direction from terminal C 20 to terminal D 22 will divide between the two respective windings, i.e., a first portion of the current will flow through a first half 50 of the winding, and a second portion of the current will flow through a second half 52 of the winding. The current which flows through the first half 50 of the winding has a current direction into the plane of the toroid 10, at its inner radius. The current which flows through the second half 52 of the winding has a current direction out of the plane of the toroid 10, at its inner radius. These two current directions are in opposite directions.

If the direction of the current is reversed the direction of the motion of the rotor will likewise be reversed.

Referring to Fig. 3D, a current flowing in a direction from terminal D 22 to terminal C 20 will divide between the two respective windings, i.e., a first portion of the current will flow through a first half 50 of the winding, and a second portion of the current will flow through a second half 52 of the winding. The current which flows through the first half 50 of the winding has a current direction out of the plane of the toroid 10, at its inner radius. The current which flows through the second half 52 of the winding has a current direction into the plane of the toroid 10, at its inner radius. These two current directions are in opposite directions.

Referring once again to Fig. 1 by changing the points at which current is introduced into the winding continuous rotation of magnet 12 may be achieved in particular, for rotation in a first direction, commutation would be performed in a sequence given in Table 1: Current flows into Terminal A Produces rotation over and out of Terminal B a first 90 degrees Current flows into Terminal D Produces rotation from and out of Terminal C 90 degrees to 180 degrees Current flows into Terminal B Produces rotation from and out of Terminal A 180 degrees to 270 degrees Current flows into Terminal C Produces rotation from and out of Terminal D 270 degrees to 360 degrees Table 1 In a similar manner, rotation of magnet 12 may be achieved in an opposite direction by reversing the direction of commutation, as given in Table 2.

Current flows into Terminal A Produces rotation over and out of Terminal B a first -90 degrees Current flows into Terminal C Produces rotation from and out of Terminal D -90 degrees to -180 degrees Current flows into Terminal B Produces rotation from and out of Terminal A -180 degrees to -270 degrees Current flow into Terminal D Produces rotation fro and out of Terminal C -270 degress to -360 degrees Table 2 The above described commutation may be performed by any of a wide variety of techniques, including the use of a microprocessor and associated electronic driving circuits, as are well known to one of ordinary skill in the art.

The torque produced by the foregoing described apparatus of Fig. 1 can be made constant if the rotor poles never overlap the current injection points, i.e., the rotor poles must span less than 90 degrees, minus the commutation (or current switching) accuracy.

The foregoing described configuration is capable of producing rotation at a constant torque over 360 degrees, in a configuration requiring half of the total amount of wire as was previously necessary in a configuration requiring two separate windings. The foregoing described configuration thereby allows for the doubling of the potential torque available by allowing space previously occupied by the second winding to be effectively used to produce torque according to the present invention.

Alternately, for equal torque, the foregoing described embodment only requires half the number of wound turns, thus reducing the cost of the wire and winding it. In addition, as the wire will occupy less space in a gap between the rotor and stator, the gap can be made shorter, which results in a requirement for less magnetic material, thus again reducing cost. In further addition, the rotor can be made somewhat longer, thus increasing torque. Alternatively, larger diameter wire can be used, reducing the resistance of the winding thus improving efficiency.

Fig. 4 illustrates an alternate embodiment of the present invention. Fig. 4 is similar to Fig. 1 with respect to toroidal ring material 10, and magnet 12 pivoted for rotation about center point 14. However, the manner in which wire 16 is wound about toroidal ring material 10 differs from that discussed with respect to Fig. 1.

In accordance with the present embodiment, four identical coils, 70, 72, 74 and 76 are wound about toroidal ring material 10, occupying the four quadrants of the motor core. Two effective windings are then formed by connecting in series the two coils in opposite quadrants, in a sense such that the magnetic flux produced by one coil will be in opposition to that produced by the other coil in the opposite quadrant.

Referring to Fig. 4, a first winding 70 is wound about one quadrant of toroidai ring material 10, a second winding 72 is wound about an opposite quadrant of toroidal ring material 10, a third winding 74 is wound about a third quadrant of toroidal ring material 10 and a fourth winding 76 is wound about a fourth quadrant of toroidal ring material 10. Windings 70 and 72 are connected together in series to form a first effective winding having terminals G 84 and H 86, in such a sense that the magnetic flux produced by winding 70 in response to a current passing therethrough will be in opposition to that produced by winding 72.In a similar manner, windings 74 and 76 are connected in series to form a second effective winding having terminals E 80 and F 82, in such a sense that the magnetic flux produced by winding 74 in response to a current passing therethrough will be in opposition to the magnetic flux produced by winding 76.

The motor illustrated in Fig. 4 operates in the following manner. Current is supplied to both sets of effective windings simultaneously. This creates the same effect as previously discussed with respect to Figs. 1, 2A and 2B, and is broadly illustrated in Figs. 5A, 5B, 5C and 5D. Figs.

5A, 5B, 5C and 5D are similar to Fig. 4, and like elements have been given corresponding reference designators. For the purposes of clarity, however, magnet 12 is not illustrated.

Referring first to Fig. 5A, a current flowing in a direction from terminal E 80, through windings 76 and 74 and out of terminal F 82 will produce current in a first direction 90 and current in a second direction 92 in the plane of the toroid, at its inner radius. Windings 76 and 74 are connected in such a sense such that the current direction in winding 76 is opposite to that in 74, in the plane of the toroid, at its inner radius.

In a similar manner, a current in a direction from terminal H86, through windings 72 and 70 and out of terminal G84 will produce current in a first direction 94 and current in a second direction 96. Windings 72 and 70 are connected in a sense such that the current direction in winding 72 is opposite to that in 70, in the plane of the toroid at its inner radius. It will be noted, however, that the current directions 90 and 94 are the same, and that the current directions 92 and 96 are the same.

Consequently the resultant current directions are identical to those previously discussed with respect to Fig. 3C.

Referring next to Fig. 5B, a current flowing in a direction from terminal E 80, through windings 76 and 74 and out of terminal F 82 will produce current in a first direction 90 and current in a second direction 92 in the plane of the toroid, at its inner radius. Windings 76 and 74 are connected in such a sense such that the current direction in winding 76 is opposite to that in 74, in the plane of the toroid, at its inner radius.

In a similar manner, a current in a direction from terminal G84, through windings 70 and 72 and out of terminal H86 will produce current in a first direction 98 and current in a second direction 100. Windings 70 and 72 are connected in a sense such that the current direction in winding 70 is opposite to that in 72, in the plane of the toroid at its inner radius. It will be noted, however, that the current directions 90 and 98 are the same, and that the current directions 92 and 100 are the same.

Consequently the resultant current directions are identical to those previously discussed with respect to Fig. 3A.

Referring next to Fig. 5C, a current flowing in a direction from terminal F 82, through windings 74 and 76 and out of terminal E 80 will produce current in a first direction 102 and current in a second direction 104 in the plane of the toroid, at its inner radius. Windings 74 and 76 are connected in such a sense such that the current direction in winding 74 is opposite to that in 76, in the plane of the toroid, at its inner radius.

In a similar manner, a current in a direction from terminal H86, through windings 72 and 70 and out of terminal G84 will produce current in a first direction 94 and current in a second direction 96. Windings 70 and 72 are connected in a sense such that the current direction in winding 70 is opposite to that in 72, in the plane of the toroid at its inner radius. It will be noted, however, that the current directions 94 and 102 are the same, and that the current directions 104 and 96 are the same.

Consequently the resultant current directions are identical to those previously discussed with respect to Fig. 3B.

Referring next to Fig. 5D, a current flowing in a direction from terminal F 82, through windings 74 and 76 and out of terminal E 80 will produce current in a first direction 102 and current in a second direction 104 in the plane of the toroid, at its inner radius. Windings 74 and 76 are connected in such a sense such that the current direction in winding 74 is opposite to that in 76, in the plane of the toroid, at its inner radius.

In a similar manner, a current in a direction from terminal G84, through windings 70 and 72 and out of terminal H86 will produce current in a first direction 98 and current in a second direction 100. Windings 70 and 72 are connected in a sense such that the current direction in winding 70 is opposite to that in 72, in the plane of the toroid at its inner radius. It will be noted, however, that the current directions 104 and 100 are the same, and that the current directions 102 and 98 are the same.

Consequently the resultant current directions are identical to those previously discussed with respect to Fig. 3D.

By changing the points at which current is introduced into the winding continuous rotation of magnet 12 maybe achieved in particular, for rotation in a first direction, commutation would be performed in a sequence given in Table 3.

Current flows into terminal Produces rotation over E 80 and out of terminal F 82, a first 90 degrees.

and Current flows into terminal G 84 and out of terminal H86.

Current flows into terminal Produces rotation from F 82 and out of terminal 90 degrees to 180 degrees E 80, and Current flows into terminal G 84 and out of terminal H 86 Current flows into terminal Produces rotation from F 82 and out of terminal E 80, 180 degrees to 270 degrees.

and Current flows into terminal H 86 and out of terminal G 84 Current flows into terminal Produces rotation from E80 and out of terminal 270 degrees to 360 F 82, and degrees.

Current flows into terminal H 86 and out of terminal G 84 Table 3 In a similar manner, rotation may be achieved in an opposite direction by reversing the direction of commutation, as given in Table 4.

Current flows into terminal Produces rotation over E 80 and out of terminal a first 90 degrees F 82 and Current flows into terminal G 84 and out of terminal H 86 Current flows into terminal Produces rotation from E 80 and out of terminal -90 degrees to - 180 F 82, and degrees Current flows into terminal H 86 and out of terminal G 84 Current flows into terminal Produces rotation from F 82 and out of terminal -180 degrees to -270 E 80, and degrees Current flows into terminal H 86 and out of terminal G 84 Current flows into terminal Produces rotation from F 82 and out of terminal -270 degrees to 360 E 80, and degrees Current flows into terminal G 84 and out of terminal H 86 Table 4 The above described commutation may be performed by any of a wide variety of techniques, including the use of a microprocessor and associated electronic driving circuits, as are well known to one of ordinary skill in the art.

The foregoing described configuration of Fig. 4 results in a configuration requiring half of the amount of current to be passed through each of the effective windings as was required with the configuration of Fig. 1, to produce the same amount of torque. In particular, only half the amount of the current which was required to be passed through one of the coils discussed with the configuration of Fig. 1 is required to be passed through each of the effective windings of the configuration of Fig. 4. Consequently, the associated electronics necessary to supply current to the effective windings of the configuration of Fig. 4 need only be capable of handling half of the current of the associated electronics necessary to supply current to the windings of the configuration of Fig. 1. Consequently, the reliability of the associated electronics is improved, or alternatively, the associated electronics can be made smaller, or a combination of both.

While the present invention was described with respect to the particular embodiments illustrated in the foregoing figures, it will be understood that other equivalent embodiments would be apparent to one of ordinary skill in the art, and are intended to be included within the spirit of the present invention. Consequently, the scope of the present invention is to be limited only by the following claims.

Claims

1. Apparatus for producing motion, comprising: magnetic flux means having a first and second ends for producing magnetic flux between the ends, mounted for movement about a selected point: magnetic conduction means surrounding said magnetic flux means for providing a path for the magnetic flux between the ends of said magnetic flux means; single electric conduction means, wound around said magnetic conduction means, for providing a continuous path for electric current around said magnetic conduction means; and, coupling means for introducing electric current into said electric conduction means from selected positions thereon.

2. Apparatus as recited in claim 1, wherein said magnetic flux means is a bar magnet.

3. Apparatus as recited in claim 2, wherein said bar magnet is mounted for rotational movement about a center point thereon.

4. Apparatus as recited in claim 3, wherein said bar magnet is made from neodynium or samarium cobalt.

5. Apparatus as recited in claim 1, wherein said magnetic conduction means is composed of soft magnetic permeable material formed in the shape of a torodial ring.

6. Apparatus as recited in claim 1, wherein said electric conduction means is an electrical conductor forming a single closed electrical path around said magnetic conduction means.

7. Apparatus as recited in claim 1, wherein said coupling means comprises a plurality of electrical taps onto said electrical conduction means at equal distances apart.

8. Apparatus as recited in claim 7, wherein said plurality of electrical taps comprises a total of four electrical taps.

9. Apparatus for producing motion, comprising: a magnet, pivoted for rotation about a center point, and having a first and second end for producing magnetic flux between the ends thereof; a ring surrounding said magnet, comprised of a mild steel toroidal core, for providing a path for the magnetic flux between the ends of said magnet; a single continuous winding around said ring so as to form a continuous electrical circuit; connection points to said winding for coupling electrical currents to and from selected portions of said winding, for the production of required current flow pattern.

10. Apparatus as recited in claim 9, wherein said connection points further comprise a total of four connection points, spaced around said ring at ninety degree intervals.

11. Apparatus as recited in claim 10, wherein said bar magnet is made from neodynium or samarium cobalt.

12. Apparatus for production of motion, comprising: magnetic flux means having a first and second end for producing magnetic flux between the ends, mounted for movement about a selected position; magnetic conduction means surrounding said magnetic flux means, for providing a path for the magnetic flux between the ends of said magnetic flux means;; a plurality of electric conduction means, each wound around said magnetic conduction means and positioned at equal distances therearound, for providing a plurality of paths for electric current around said magnetic conduction means, with electric conduction means on opposing sides of said magnetic conduction means being coupled together in series in a sense such that in response to an electric current being passed therethrough, magnetic flux produced by one electric conduction means will be in an opposite direction to magnetic flux produced by the other.

13. Apparatus as recited in claim 12, wherein said magnetic flux means is a bar magnet.

14. Apparatus as recited in claim 13, wherein said bar magnet is mounted for rotational movement about a center point thereon.

15. Apparatus as recited in claim 14, wherein said bar magnet is made from neodynium or samarium cobalt.

16. Apparatus as recited in claim 12, wherein said magnetic conduction means is composed of soft magnetic permeable material formed in the shape of a torodial ring.

17. Apparatus as recited in claim 12, wherein said pluraity of electric conduction means is comprised of a plurality of electrical windings, positioned at equal distances about said magnetic conduction means, with electrical windings on opposite sides of said magnetic conduction means being connected in series in a sense such that in response to a current being passed therethrough, magnetic flux produced by one winding will be in an opposite direction to magnetic flux produced by the winding on the opposite side.

18. Apparatus as recited in claim 17, wherein said plurality of electrical windings is comprised of four electrical windings.

19. Apparatus for producing motion, comprising: a magnet, pivoted for rotation about a center point, and having a first and second end, for producing magnetix flux between the ends thereof; a ring surrounding said magnet, comprises of a mild steel torodial core, for providing a path for the magnetic flux between the ends of said magnet; a plurality of windings positioned at equal distances around said ring, with windings on opposite sides connected in series in a sense such that magnetic flux produced in response to a current passing through the windings will be in opposite directions.

20. Apparatus as recited in claim 19, wherein said plurality of windings comprise four windings.

21. Apparatus as recited in claim 19, wherein said magnet is made from neodynium of samarium cobalt.

22. Apparatus for producing motion substantially as hereinbefore described with reference to and as illustrated in Figs. 4 to 5D of the accompanying drawings

22. Apparatus for producing motion substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 3D or in Figs. 4 to 5D of the accompanying drawings.

CLAIMS New claims or amendments to claims filed on 1 7 Dec 86 Superseded claims 1 to 11, 22 New or amended claims:

1. Apparatus for producing motion comprising: magnetic flux means having a first and second ends for producing magnetic flux between the ends, mounted for movement about a selected point; magnetic conduction means, in the form of a toroidal ring of soft magnetic permeable material, surrounding said magnetic flux means for providing a path for the magnetic flux between the ends of the magnetic flux means; single electric conduction means, wound unidirectionally around said ring for providing a continuous path for electric current around the ring; and coupling means for introducing electric current into the electric conduction means from selected positions thereon.

2. Apparatus as claimed in claim 1 wherein the magnetic flux means is a bar magnet.

3. Apparatus as claim 2 wherein the bar magnet is mounted for rotational movement about a centre point thereon,

4. Apparatus as claimed in claim 2 or 3 wherein the bar magnet is made from neodynium or samarium cobalt.

5. Apparatus as claimed in any preceding claim wherein the electric conduction means is an electrical conductor forming a single closed electrical path around the ring.

6. Apparatus as claimed in any preceding claim wherein the coupling means comprises a pluraity of electrical taps onto the electrical conduction means at equal distances apart.

7. Apparatus as claimed in claim 6 wherein said plurality of electrical taps comprises a total of four electrical taps.

8. Apparatus for producing motion comprising: a magnet, pivoted for rotation about a centre point and having a first end and a second end, for producing magnetic flux between the ends thereof; a ring surrounding said magnet and in the form of a mild steel toroidal core, for providing a path for the magnetic flux between the ends of the magnet; a single continuous winding wound unidirectionally around said ring so as to form a continuous electrical circuit; and connection points to the winding for coupling electrical currents to and from selected portions of said winding, for the production of a current flow pattern.

9. Apparatus as claimed in claim 8, wherein said connection points further comprise a total of four connection points, spaced round said ring at ninety degree intervals.

10. Apparatus as claimed in claim 9, wherein said bar magnet is made from neodynium or samarium cobalt.

11. Apparatus for producing motion substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 3D of the accompanying drawings.