GB2311172A - Low-torque,interchangable-rotor electric motor - Google Patents

Abstract

The stator of an electric motor is provided by coils 22 disposed in an interrupted-annular array about a central space such that a path A through the array is provided whereby a selected one of a plurality of rotors 21 can be moved in the plane of and through the array into and out of said central space. In the preferred embodiment each rotor 21 is a gobo freely rotatable on a wheel which can be indeed to bring it into a light path, when it will be positioned to be rotated when the coils 22 are energised. The non-annular disposition of the coils 22 results in a motor of low torque but it is is adequate to rotate a gobo disc, which is simply a perforated sheet of metal. As applied to a disco lighting unit the motor of the invention provides a much cheaper and simpler drive arrangement for gobo discs.

Description

This invention relates to a low-torque, interchangeable-rotor electric motor particularly although nat exclusively suitable for rotating gobo discs in a lighting effect unit.

In places of public entertainnfnt, particularly discotheques, light beams are used to create atnDsphere and promote a pleasurable and exciting eronixxlment, for example for dancing. Using mirrors, colour filters and nçvement diverse effects are created, far example with rotating beams of coloured light.

Patterns can be created using so-called gobo discs, which are in effect stencils interposed in the light beams. A gobo disc masks the associated light beam except where a pattern is cut out of the disc, such as a starshaped aperture in the disc. Where several such patterns are provided on the sank gobo disc a pleasing effect is created by rotating the disc.

Usually several different gobo discs together with other effects such as colour filters or shutters are distributed in respective apertures circumferentially of a carrier wheel. This is rotatable to index the selected one of the gobo discs or the like into the path of the associated light beam. At present gobo discs to be rotated are located in respective carrier rings which have toothed peripheries engaging a sun gear coaxial with the carrier wheel, so that rotation of the sun gear relative to the carrier wheel rotates each gobo disc in its carrier ring. A carrier ring for a gobo disc has been thought necessary because of the light construction of the latter, usually fran thin sheet metal. It would not be practicable to form the gobo disc itself with gear teeth by which it might be driven.

The provision of the toothed carrier rings for the gobo discs, the sun gear and its drive and bearings represent a high manufacturing cost which has a considerable inpact on the price of a lighting effect unit as a whole.

Moreover the gears are required to work in a high temperature environment because of the proximity of a high-pcwer light source in an enclosed housing and this leads at best to a short working life and at worst to break down and failure for example because of lubrication problems.

An object of the present invention is to offer remedies to the problems currently associated with the rotation of gobo discs and to reduce manufacturing costs while enhancing reliability.

According to the invention this object can be achieved by using a gobo disc to be rotated as the rotor of an electric motor, the stator being provided by coils disposed on a fixed mounting about the freely rotatable gobo disc.

Traditionally the element or elements providing the stator of an electric motor are in an annular array which is as carplete as possible. There has been no motivation deliberately to provide gaps in the array because these would reduce the torque output of the motor.

However in a lighting effect unit as aforedescribed it is desired to move gobo discs through and in the plane of any array of stator elements used to rotate them.

The present invention proceeds fran the realisation that because of the very light weight of a gobo disc it may be spun effectively by an electric motor of low torque. Therefore it is acceptable to anit stator elements fran the annular array thereof which would otherwise obstruct indexing movement of a gobo disc on the carrier ring into and out of a position in which the gobo disc will serve as the rotor of the motor.

A further and subsidiary feature of the present invention is to render a gobo disc suitable as the rotor of an electric motor by giving it a toothed periphery. This is not the only way in which the periphery of a gobo disc could be given the necessary characteristic of being magnetically discontinuous. For example a non-ferrcus, e.g. plastics, gobo disc might be provided peripherally with mutually spaced ferrous inserts. However the toothed periphery is the preferred option because it is easier and cheaper to make and has the added benefit of further reducing the weight of the gobo disc.

In accordance with the present invention there is provided a low-torque, interchangeable rotor electric motor in which the stator is provided by coils disposed in an interrupted-annular array about a central space such that a path through the array is provided whereby a selected one of a plurality of rotors can be mooted in the plane of and through the array into and out of said central space.

The said path preferably traverses the array such that a rotor can be moved in the sazre direction both into and out of said central space.

The coils may be distributed about an aperture in a mounting such that said central space is in alignment with the said aperture and a carrier for the rotors may be provided which is rotatable relative to the mounting, the carrier having at substantially equal distances from its axis of rotation a plurality of rotor elements distributed circumferent;^lly of the carrier, each said rotor element being rotatable relative to the carrier.

Each rotor element may be rotatable on a respective stem which extends fran a side of the carrier nearer to the mounting, each said stem being mounted centrally of an aperture in the carrier aligned with the respective rotor.

When the motor of the two inmediately preceding paragraphs is used in a lighting effect unit which also comprises a light source and at least one lens spaced from the light source along a light path, preferably the carrier and the mounting are disposed substantially parallel with one another between said lens and the light source such that said central space is in said light path and indexing rotation of the carrier may bring any one of the rotors thereon into and out of said light path.

The e end of each stem remote fran its respective rotor may be mounted on a crossemember arrangement spanning the aperture in the carrier associated with said stem and the arrangement may be such that light fran the light source is more focused on said lens than on said cross-medber arrangement, when disposed in the light path, such that said lens and any additional lenses downstream thereof in the light path will not provide a sharply defined image of the cXoss-member arrangement.

Each rotor may be a gobo disc which has a magnetically discontinuous periphery such that it will be rotated by the coils when located in said central space and when the coils are sequentially energised.

Preferably each gobo disc has a toothed periphery whereby it is magnetically discontinusus.

By a "magnetically discontinuous periphery" is meant that magnetic attractance is not uniform circumferentially of the gaho disc. If the disc is of magnetisable metal this can be achieved by giving the disc a toothed periphery. However if it is not the same effect could be achieved, for example, by positioning elements of magnetisable metal in circumferentially spaced locations around the periphery of a circular, non-magnetiseable disc.

A preferred embodiment of the invention will now be described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a partial view of a carrier wheel formed peripherally with apertures in one of which a mounting for the bearing of a gobo disc is located, Figure 2 illustrates a motor in accordance with the present invention, and Figure 3 is a sectional elevation of a lighting effect assembly incorporating the motor of the invention.

Referring first to Figure 3, a lighting effect unit comprises a light source 10 the light from which is focused by a ref lector 11 generally at a lens 12.

The e lens 12 spans an aperture 13 in a fixed plate 14 carrying a conventional electric motor 15. A main gobo wheel 16 is rotatable by motor 15 via a shaft 17. As is knawn per se and as illustrated in Figure 1 the gobo wheel 16 has circumferentially distributed apertures 18 which, by indexing movement effected by the motor 15, can be brought in sequence into slignment with the aperture 13. If each of the apertures 18 is associated with a different gobo disc different light effects can be provided by suitable indexing rotation of wheel 16. One or more additional wheels (not shown) interposed between light source 10 and lens 12 may carry other effects such as colour filters. A shutter (not shown) may also be provided.

In accordance with the present invention the aperture 18A in wheel 16 is spanned by a cross-strut 19 which serves as a mounting for one end of a bearing pin 20. The other end of pin 20 rotatably carries a gobo disc 21 so that the latter is coaxial with aperture 18A and is spaced by the length of pin 20 from wheel 16 toward fixed plate 14.

Mbunted on fixed plate 14 to be distributed around aperture 13 are coils 22.

The disposition of the coils 22 is such that an arcuate path A exists between them, this being the path which will be swept by gobo disc 21 wlhen the carrier ring 16 is rotated. The gobo dise 21, which is stamped out of thin sheet metal, has a toothed periphery as seen in Figure 2. The angular separation of the teeth is related to the angular separation of the coils 22 such that when the coils 22 are sequentially energised they will produce a variable reluctance field which will cause the gobo dise 21 to spin on pin 20.

It is within the competence of the skilled person to vary the number and angular separation of the coils 22 as well as the design of the perery of the disc 21 to achieve optimum results in terms of the rotation and control of the disc 21. This technology is known per se from electric stepper motors so that mare detailed description is considered unnecessary except to say that the arrangement of the invention differs fran a conventional stepper motor in that it is not designed to create optimum torque. Its only purpose is to spin the disc 21 which, as previously discussed, will normally be of very light construction. The sacrifice of torque permits the arrangement of coils 22 such that they will not obstruct the movement of gobo disc 21 in path A both into and out of the central space between the coils 22.

It will be apparent that the remaining apertures 18 of wheel 16 may be associated either with similar gcbo disc arrangements or by alternative lighting effects. The e same coils 22 are, of course, used to spin any selected gobo disc or similar disc.

Claims (10)

CIAIES :

1. A low-torque, interchangeable rotor electric motor in which the stator is provided by coils disposed in an interroptei-annular array about a central space such that a path through the array is provided whereby a selected one of a plurality of rotors can be moved in the plane of and through the array into and out of said central space.

2. A motor as claimed in claim 1, wherein said path traverses the array such that a rotor can be moved in the sank direcon both into and out of said central space.

3. A motor as claimed in claim 1 or claim 2, wherein the coils are distributed about an aperture in a mounting such that said central space is in alignment with the said aperture and wherein a carrier for the rotors is provided which is rotatable relative to the mounting, the carrier having at substantially equal distances from its axis of rotation a plurality of rotor elements distributed circumferentially of the carrier, each said rotor element being rotatable relative to the carrier.

4. A motor as claimed in claim 3, wherein each rotor element is rotatable on a respective stem which extends from a side of the carrier nearer to the mounting, each said stem being mounted centrally of an aperture in the carrier aligned with the respective rotor.

5. A motor as claimed in claim 4 when used in a lighting effect unit which also comprises a light source and at least one lens spaced fran the light source along a light path, wherein the carrier and the mounting are disposed substantially parallel with one another between said lens and the light source such that said central space is in said light path and indexing rotation of the carrier may bring any one of the rotors thereon into and out of said light path.

6. A motor as claimed in claim 5, wherein the end of each stem remote fran its respective rotor is mounted on a cross-member arrangement spanning the aperture in the carrier associated with said stem and wherein the arrangement is such that light from the light source is more focused on said lens than on said cross-nEmber arrangement, when disposed in the light path, such that said lens and any additional lenses downstream thereof in the light path will not provide a sharply defined image of the cross-meer arrangement.

7. A motor as claimed in claim 6, wherein each rotor is a gobo disc which has a magnetically discontinuous periphery such that it will be rotated by the coils when located in said central space and when the coils are sequentially energised.

8. A motor as clainred in claim 7, wherein each gobo disc has a toothed periphery whereby it is magnetlallly discontinuous.

9. A low-torque, interchangeable-rotor electric motor substantially as hereinbefore described with reference to and as shown in the accompanying Drawings.

10. A lighting effect unit incorporating a motor as claimed in any one of the preceding claims substantially as hereinbefore described with reference to and as shown in the acoarparying Drawings.