GB2294161A - Rotor - Google Patents

Abstract

A wholly or substantially magnetically non-conducting rotor for a motor, on and around which rotor is located one or more asymmetric and/or outstanding magnetically conducting elements adapted to cause rotation of the rotor by one or more magnets located therearound in use is described herein. The rotor is suitable for use in stepping motors using electro magnets, movable permanent magnets or magnetic shields. Fig. 7a shows an arrangement permitting reverse rotation. Asymetric electromagnet disposition is disclosed (Fig. 5A - C). <IMAGE>

Description

ROTOR FOR ELECTRIC MOTORS This invention relates to a rotor, particularly but not exclusively for stepping motors.

Stepping motors translate electrical pulses into mechanical movement. Variable reluctance stepping motors generally comprise a central metallic 'toothed' rotor surrounded by a stator having a multiplicity of opposing electromagnets, also called "teeth". As each set of stator teeth is excited to produce a magnetic field across the rotor, the nearest rotor teeth rotate to align themselves with the magnetic field and thereby reduce the magnetic reluctance of the field to a minimum. As current is switched to the next set of stator teeth, the rotor rotates further. Continual switching, or "phasing" of the current to different teeth produces continual rotation of the rotor, which then acts as or is connected to the drive-shaft of the motor. The rotation of the rotor is a series of discrete identical steps.

However, solid metallic rotors are heavy and substantial inertia must be overcome to initiate and maintain their rotation. This also limits the step angle (angle of rotation of the rotor between each switch of the magnetic field). Usually, a large number of phase switches are required for a complete revolution of the rotor. This requires a large number of stator teeth with corresponding wiring and switching mechanisms. The rotor is also completely symmetric about its centre.

According to an aspect of the present invention, there is provided a wholly or substantially magnetically non-conducting rotor for a motor, on and around which rotor is located one or more asymmetric and/or outstanding magnetically conducting elements adapted to cause rotation of the rotor by one or more magnets located therearound in use.

The or each element is "asymmetric" as it extends around and/or is outstanding from the cylindrical plane of the rotor about the rotor's rotational axis. The asymmetric elements may be of any shape which is asymmetric, e.g. having a taper therein.

Preferably, such elements taper symmetrically from one end to the other, and they may taper either in width or in height, or both. The or each element may have separated ends about the rotor. Preferably, they are so arranged as to form a continuous 'ring' about the rotor. The outstanding elements are spaced increasingly from the rotor along their length. The elements may be sequentially or asequentially located around the rotor.

The or each magnet may be a permanent magnet or an electromagnet. Where a plurality of magnets are used, they may be located symmetrically or asymmetrically around the rotor, that is the poles of the magnets may be on opposite sides of the rotor, or on the same side of the rotor, or positioned at any angle thereinbetween (as long as they are closer to the rotor than each other). One or more of the magnets may be moveable to assist the rotation of the rotor. Where an asymmetrical arrangement of a plurality of magnets is used, the step angles may be irregular as compared with a symmetrical arrangement.

As the rotor in the present invention is not a conductor, it need not be made from a high-permeability and heavy material such as metal. It may be made from e.g. a lightweight plastic. This can considerably reduce the weight of the rotor, hence reducing the inertia of the rotor. As the rotor of the present invention requires less energy to initiate and continue its rotation, any motor using it, e.g. a stepping motor, is more efficient. '.

The lighter rotor is also more sensitive to magnetic fields and magnetic field changes. Thus the step angle for the rotor of a stepping motor may be greater than that of conventional metallic rotors, although small step angles may still be used where desired or necessary. A greater step angle decreases the number of teeth required.

Reducing the number of teeth reduces the possible size and weight of the motor, and also reduces the complexity of the wiring and phase switch mechanisms required. The rotor also allows greater flexibility in the step angle necessary or desired.

The rotor of the present invention may be used in any suitable motor requiring or providing rotational motion, e.g. a drive-shaft.

According to a second aspect of the present invention, there is provided a stepping motor comprising a rotor as defined above on and around which a plurality of asymmetrical and tapering elongate magnetically conducting elements are located, and a plurality of sets of electromagnets around the rotor, wherein in use a current is sequentially applied to each set of electromagnets to create a magnetic field thereinbetween causing the rotor to rotate as the broadest parts of the elements follow the moving magnetic field.

In this aspect, the energy or magnetic reluctance in an applied magnetic field is reduced as the amount of magnetically conducting material aligned in the magnetic field increases. Thus alignment of the maximum amount of magnetically conducting material, i.e. the broadest or more extensive parts of the elements, with the magnetic field will reduce the magnetic reluctance to the greatest extent. As the magnetic field then moves, the broadest parts of the elements therefore follow it. The elements thus follow the sequential steps of the applied magnetic field.

Where the elements are sequentially located about the rotor (i.e. 'head-to-toe'), the rotor will rotate in one direction. Location of the elements 'head-to-head' allows rotation of the rotor in either direction.

According to another aspect of the present invention, there is provided a stepping motor comprising a rotor as defined above on and around which a plurality of oustanding magnetically conducting elements are located, and a plurality of sets of electromagnets around the rotor, wherein in use a current is sequentially applied to each set of electromagnets to create a magnetic field thereinbetween causing the rotor to rotate as the closest parts of the elements to the electromagnets follow the moving magnetic afield.

The energy or magnetic reluctance in an applied magnetic field is reduced as the distance between the outstanding magnetically conducting material on the rotor and the electromagnets creating the magnetic field decreases, i.e. as the air gap over which the magnetic flux must 'jump' decreases. Thus alignment of the parts of the elements that can become closest to the electromagnets with the magnetic field will reduce the magnetic reluctance to the greatest extent. As the magnetic field then moves, the 'closest' parts of the elements therefore follow it. This effect also occurs by the use of elements tapering in width as described above. The thick ends of such elements extend further out from the rotor than the thin ends. The thick ends can therefore become closer to the electromagnets than the thin ends.

The elements for use with a stepping motor using a rotor of the present invention may be a combination of the features of both embodiments described above, e.g. the elements taper both in width and in height, and they extend outwardly from the rotor from the narrow and thin end of the taper to the wide and thick end. Preferably the stepping motor comprises two tapering elements which symmetrically and substantially surround the rotor, and two sets of opposing electromagnets.

According to a further aspect of the present invention, there is provided a motor comprising a rotor as defined above on and around which is located one or more tapering elongate elements, and one or more permanent magnets therearound adapted to cause rotation of the rotor. The permanent magnet(s) may cause rotation of the rotor by movement or repositioning of the magnet(s) around the rotor ahead of the broadest or most extensive part of the element(s) such that that part of the or each element follows it. Alternatively, the magnetic field of the permanent magnet(s) can be blocked with a material that is not attracted to the magnetic field, e.g. using a superconductor. This arrangement blocks out the magnetic field(s) at the areas where the rotor would normally come to rest, thus allowing the rotor to continue to rotate past these points.

A number of the motors of the present invention may be aligned to produce greater power therefrom.

Embodiments of the present invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which: Figs. 1, 2, 3a and 3b are perspective views of rotors according to different embodiments of the present invention; Figs. 4a-4c, 5a - Sc and 7a - 7c are schematic plan views of three different stepping motors according to other aspects of the present invention; Figs. 6a-6c are schematic plan views of a motor according to another aspect of the present invention; and Fig. 6d is a side view of the motor of Figs. 6a-6c.

Referring to the drawings, Fig. 1 shows a first rotor 2 made from a lightweight plastic material having a core 4 for an axle (not shown). Around the side of the rotor 2 are two tapering elongate magnetically conducting elements 5,6. The tapering elements 5,6 are asymmetric around the cylindrical plane of the rotor 2. The elements 5,6 taper in height symmetrically from one end to the other. In Fig. 1, the narrow end 8 of element 5 and the wide end 10 of element 6 are visible. The elements 5,6 are located symmetrically on and around the side of the rotor 2 about the axis of the core 4.

Fig. 2 shows a second rotor 12 around which there is a series of tapering elongate magnetically conducting elements 14. The elements 14 taper in width from a thick end 16 to a thin end 18. The elements 14 are located symmetrically on and around the rotor 12 about axis 19.

Fig. 3a shows a third rotor 20 around which there is a series of outstanding magnetically conducting elements 22 located symmetrically about the axis 24 of the rotor 20. Each element 22 is spaced increasingly from the rotor 20 along its length from an attached end 25 to a "free" end 26. If necessary or desired, each free end 26 could be supported to assist maintenance of its position, e.g. by placing suitable wedges underneath each element 22.

Fig. 3b shows a fourth rotor 28 wherein the free ends 26 of the separate elements 22 on the rotor 20 in Fig. 3a are conjoined with the attached ends 25 of the next elements 22 by magnetically conductible material, so as to form a continuous 'ring' 29 about the rotor 28.

Figs 4a-4c are plan views of a stepping motor comprising a rotor 30 having two magnetic ally conducting elements 32, 34 therearound and two sets of symmetrically located and opposing electromagnets 35,36 and 37,38. The wiring and switching mechanisms for the electromagnets are not shown. On rotor 30, elements 32,34 are shaded from heavy to light to illustrate the tapering of the height of the elements 32,34 from their wide ends 40,41 to their narrow ends 42,43. The elements 32,34 also taper in width as shown. Thus the elements 32,34 are a combination of the shapes of the elements shown in Figs. I and 2 above.

Taking the configuration of the motor in Fig. 4a as a rest position, electromagnets 35 and 36 are excited ("Phase 1"), creating a magnetic field thereinbetween. In order to reduce the magnetic reluctance to the lowest possible minimum, those parts of the elements 32,34 having the greater amount of magnetically conducting material, and able to be closer to the electromagnets 35,36, i.e. the wide and thick ends 40,41, are attracted towards the magnetic field in order to align themselves therewith. Thus the rotor 30 rotates in direction 44 until it reaches a position as shown in Fig. 4b.

Once the position in Fig. 4b has been reached, or immediately prior thereto, Phase I is deactivated, and electromagnets 37,38 are activated ("Phase II") to create a magnetic field thereinbetween. As before, the wide and thick ends 40,41 of the elements 32,34 are attracted to the magnetic field, this time of Phase II, in order to reduce the magnetic reluctance to the lowest possible minimum by alignment therewith This creates further rotation of the rotor 30 in direction 44 as shown in Fig 4c. The cycle is continued by deactivation of Phase II and reactivation of Phase I and so forth.

Figs 5a - Sc are plan views of a stepping motor using the same rotor 30 as the motor in Figs. 4a - 4c (in a reverse position) but having two sets of asymmetrically located electromagnets therearound, 46, 48 and 50, 52. Taking the configuration of the motor in Fig. 5a as an initial position, electromagnets 46, 48 are excited (Phase I) causing rotation of the rotor 30 (for the reasons described above) in direction 54 until it reaches a position as shown in Fig. 5b. Following deactivation of Phase I, electromagnets 50, 52 are excited (Phase II) to rotate the rotor 30 further in direction 54 to a position as shown in Fig. 5c. As the position in Fig. Sc corresponds to that in Fig.

5a, deactivation of Phase II and reactivation of Phase I will create further revolution of the rotor 30.

Figs. 6a-6c are plan views of a motor comprising a rotor 56 having one element 58 therearound and on one side of the rotor 56 a U-shaped permanent magnet 60. The element 58 is similar to one of the elements (32,34) as shown in Fig. 4a, i.e. it tapers both in height (as shaded) and width, although it extends around the whole of the rotor 56.

Taking the configuration of the motor in Fig. 6a as an initial position, the rotor 56 rotates in direction 62 until it reaches a position as shown in Fig. 6b in order to reduce the magnetic reluctance to the lowest possible minimum by having the greatest amount of magnetically conducting material of the element 58 within the magnetic field of the magnet 60. The magnet 60 is then moved to the opposite side of the rotor 56 as shown in Fig. 6c, which causes further rotation of the rotor 56 in direction 62 for the reason described above. Further movement of the magnet 60 causes further rotation of the rotor 56. Fig. 6d is a side view of the motor of Figs. 6a-6c.

Figs. 7a-7c are plan views of a stepping motor comprising a rotor 64 located around which are four magnetically conducting elements 66,67,68,69, similar in shape to the elements (32, 34) in Fig. 4a, and four of sets of opposing electromagnets, 71 and 72, 73 and 74, 75 and 76, and 77 and 78. The elements 66-69 are located 'head-to-head' about the rotor 64. Taking Fig 7a as a starting position, activation of magnets 71 and 72 rotates the rotor 64 in direction 80 to the position shown in Fig 7b. These electromagnets 71,72 are then deactivated and magnets 73 and 74 activated. The rotor 64 now rotates in direction 80 to the position shown in Fig 7c. Continuing the sequence by deactivating magnets 73 and 74 and activating magnets 75 and 76, and then deactivating magnets 75 and 76, and activating magnets 77 and 78, will allow a half revolution of the rotor 64. Repeating this whole sequence will allow a complete revolution of the rotor 64. Similarly, from the starting position shown in Fig 7a, activation of magnets 75 and 76, then magnets 73 and 74, then magnets 71 and 72 and then magnets 77 and 78 will allow a half revolution of the rotor 64 in the opposite direction. Repeating this sequence will allow a complete revolution in the opposite direction.

Variations and modifications can be made without departing from the scope of the invention as described above and as claimed hereinafter.

Claims (23)

1. A wholly or substantially magnetically non-conducting rotor for a motor, on and around which rotor is located one or more asymmetric and/or outstanding magnetically conducting elements adapted to cause rotation of the rotor by one or more magnets located therearound in use.

2. A rotor as claimed in Claim 1 wherein the or each asymmetric element tapers in height.

3. A rotor as claimed in Claim 1 or Claim 2 wherein the or each asymmetric element tapers in width.

4. A rotor as claimed in any one of Claims 1 to 3 wherein the elements taper symmetrically from one end to the other.

5. A rotor as claimed in any of one Claims 1 to 4 wherein the rotor is made from a lightweight plastic.

6. A motor whenever incorporating a rotor as defined in any one of Claims 1 to 5.

7. A motor as claimed in Claim 6 wherein the motor is a stepping motor comprising a rotor on and around which a plurality of asymmetrical and tapering elongate magnetically conducting elements are located, and a plurality of sets of electromagnets around the rotor, wherein in use a current is sequentially applied to each set of electromagnets to create a magnetic field thereinbetween causing the rotor to rotate as the broadest parts of the elements follow the moving magnetic field.

8. A motor as claimed in Claim 7 having two or more sets of symmetrically located and opposing electromagnets.

9. A stepping motor as claimed in Claim 7 having two or more sets of asymmetrically located electromagnets.

10. A stepping motor as claimed in any one of Claims 7 to 9 wherein the elements are located sequentially about the rotor.

11. A stepping motor as claimed in any of Claims 7 to 9 where the elements lcoated head-to-head about the rotor.

12. A motor as claimed in Claim 6 wherein the motor is a stepping motor comprising a rotor on and around which a plurality of outstanding magnetically conducting elements are located, and a plurality of sets of electromagnets around the rotor, wherein in use a current is sequentially applied to each set of electromagnets to create a magnetic field thereinbetween causing the rotor to rotate as the closest parts of the elements to the electromagnets follow the moving magnetic field.

13. A motor as claimed in Claim 6 wherein the motor comprises a rotor on and around which is located one or more tapering elongate elements, and one or more permanent magnets therearound adapted to cause rotation of the rotor.

14. A motor as claimed in Claim 13 wherein the rotor is rotated by repositioning the or each permanent magnet.

15. A motor as claimed in Claim 13 wherein the rotor is rotated by the magnetic field of the or each permanent magnet being blocked with a material that is not attracted to the magnetic field at any area where the rotor would normally come to rest.

16. A rotor as substantially herein described with reference to Fig 1.

17. A rotor as substantially herein described with reference to Fig 2.

18. A rotor as substantially herein described with reference to Fig 3a.

19. A rotor as substantially herein described with reference to Fig 3b.

20. A stepping motor as substantially herein described with reference to Figs. 4a4c.

21. A stepping motor as substantially herein described with reference to Figs. Sa-Sc

22. A motor as substantially herein described with reference to Figs. 6a-6d.

23. A stepping motor substantially herein described with reference to Figs. 7a-7c.