LIGHT-OPERATED SLIP RING

Abstract: A light-operated slip ring in which a signal is transmitted across an interface between members (1, 2) which have relative rotational motion utilizing an inclined off-axis fibre transmission line (4) on at least one member directed across a gap (5) at the interface to an on-axis fibre transmission line (3), on the other member (2) to form a continuous optical path between members during relative rotation.

Description: 1 . This invention relates to a full duplex rotating optical fibre coupling for simultaneous wide-band digital signal transmission- Various forms of such devices have been used 5 heretofore including means using light transmission and as an example reference may be had to European Patent Application No. 0.045.585 of -Texas Instruments Incorporated which relates to a device using inclined bilateral transmission means in the form of light 0 signal generating transmitting and receiving means fed by fibre optic lines and involved "active" transducers at the slip ring to produce and receive the light transmitted over the gap between a stationary and a rotating component. 5 An object of the invention is to provide a .slip ring which can be used without signal degradation in adverse environmental situations, particularly those subject to electromagnetic interference. A further object is to have a signal transmission 0 system in which two members with relative motion therebetween can transmit and receive the signal without the need to use brushes or other mechanical transmission devices or the need to use "active" transducers at the interface between members with relative rotation therebetween, and which can, when required, pass isolated signals in opposite directions between the members . A further object is to increase the number of signals which can be passed using only axial fibre optic receiving lines. The objects are achieved by using a light signal transmitted across an interface between members which have relative rotational motion about a common axis the one in relation to the other, each member having at least a fibre transmission line along which the light is transmitted from one member to the other member across a gap formed at an interface, and in the case of bilateral transmission of isolated signals in opposite direction, each member having a first on-axis fibre and a second fibre inclined to the axis, the inclined fibre being directed to direct light to the on-axis fibre at the interface to transmit a light signal from the inclined fibre line to the on-axis fibre line. In its preferred form the invention comprises a light-operated slip ring in which a signal is transmitted across an interface between a first- member and a second member which have relative rotational motion the one to the other about a common axis, characterised by at least one member carrying at least one inclined off-axis fibre transmission line along which the light is transmitted across a gap formed at the interface between the two members, and the other member carrying an on-axis fibre transmission line, the Inclined fibre transmission line being directed towards the end of the axial fibre transmission line at the interface, with each fibre transmission line terminating at the gap at the interface, whereby the fibre optic transmission lines form at least a continuous optical path between members during relative rotation. According to another embodiment the light-operated slip ring is characterised by bilateral transmission means in which each member has two fibre transmission lines with each member carrying an inclined fibre transmission line directed to an axial fibre transmission line carried by the other member. According to still another embodiment the light- operated slip ring is characterised in that at least one of the members carries a plurality of inclined fibre transmission lines directed to an axial transmission line on the other member, the inclined transmission lines being each adapted to receive different chromatic light signals, there being dichromatic filter means to separate the signals received and transmitted by the axial fibre transmission line. In order however that the invention will be fully understood an embodiment thereof will be described with reference to the accompanying drawings to which the invention is not necessarily limited and in which; FIG. 1 is a longitudinal section of a device incorporating the invention, FIG. 2 is a schematic view to demonstrate the principle of a two-way signal system showing how an inclined fibre optic transmission line is directed to an axial fibre optics receiving line in each direction. O PI FIG. 3 Is a view similar to FIG. 2 but showing how by using dichromatic means a further signal channel results, and FIG. 4 is a view similar to FIG. 2 but showing how transducers can be positioned remote from the actual slip ring itself to thereby provide a "passive" system which will not receive or emit noise, in the vicinity of the slip ring to remove or reduce noise at the gap which does not reach the gap because of the possibility of placing and possible interference sources remote from the slip ring itself. Referring first to FIG. 1, the device consists of two halves 1 and 2 of the coupling, at least one rotating collinearly about the axis of the other. Each half has two glass core optical fibres which form fibre optics transmission lines 3 and 4, which may be of 1.0 mm diameter, the first fibre transmission line 3 lies on the axis of rotation and the other fibre transmission line 4 is inclined at, for .Instance, 10° to the axis of rotation. The spacing between the pair of fibre transmission lines at each coupling face may be 0.2 mm. The two halves of the coupling have an air-gap 5 of say 3 mm between them at the coupling face, and the ends of the fibre transmission lines face each other across this air-gap 5. The other ends of the on-axis fibre transmission line 3 and the angled fibre transmission line 4 from each half of the coupling may terminate respectively in a detector 6 and a light emitting diode 7 (LED) respectively, shown more" particularly in the schematic illustration FIG. 4. Each light emitting diode 7 operates at 'different optical wavelengths, for instance 665 nm and 910 nm. These are situated sufficiently remote from the coupling interface at the air-gap 5 to avoid electrical interference. In use the input electrical digital signals are fed into a modulator 8 which pulses one of light emitting diodes 7, which is situated at the end of the inclined fibre transmission line 4 remote from the other half 1 of the coupling. Light pulses are transmitted along the inclined fibre transmission line 4 across the air-gap 5 to the on-axis fibre transmission line 3 in the rotating half 2 of the coupling. Some of this light travels along the on-axis fibre transmission line 3 to the detector 6 which converts these light pulses back into electrical signals. • • These electrical signals are fed to an amplifier 9 which converts them to electrical digital signals similar to those fed into the modulator 8. This gives one channel transmission in one direction, for instance from a fixed half 1 to a rotating half 2. Transmission in the opposite direction, from the rotating half 2 to the fixed half 1 is carried out in the same manner as for the fixed half to the rotating half. This provides for transmission of two separate channels, one in either direction at different times or simultaneous bilateral transmission of two channels. Some backscatter may be caused by some of the light pulses from the angled fibre transmission line 4 in one half of the coupling being reflected from the faces of the on-axis fibre transmission line 3 and the inclined fibre transmission line 4 in the other half of the coupling. These pulses, as indicated by the dotted line in the air-gap 5, are reflected back across the air-gap into the on-axis fibre transmission line 3 in the same half, and thereby produce an interferring signal in the detector 6 of that half. However, using light emitting diodes with different optical wavelengths and suitable wavelength blocking filters 10 at the detectors 6 reduces the effects of Backscatter to a minimum. In the form shown in FIG. 3 an added fibre signal line 12 is used which is inclined to direct the light issuing from its- end at the interface to the on-axis fibre line 3, and the on-axis fibre line has in it a dichromatic mirror 13 which separates the input from the first signal line which is the inclined fibre line 4 and the input from the second signal line which is the inclined fibre line 12 and outputs a first signal to the first signal detector 14 and a second signal to the second detector 15, blocking filters being again added if neccesary as indicated by 16 and 17. Further lines could be added. From the foregoing it will be realised that the coupling of this invention itself is a passive device which will not itself transmit or receive noise and can be used, as earlier stated herein, without signal degradation in adverse environmental situations particularly those subject to electromagnetic inter¬ ference, and is readily adapted to pass isolated signals in opposite direction, and if required in multiple form. While the specific description refers to a fixed half and a rotating half, it will be obvious that the device can be applied anywhere where there is relative motion about a common axis.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A light-operated slip ring in which a signal is transmitted across an interface between a first member and a second member which have relative rotational motion the one to the other about a common axis, characterised by at least one said member carrying at least one inclined off-axis fibre transmission line along which the light is transmitted across a gap formed at the interface between the said two members, and the other said member carries an on-axis fibre transmission line, the said Inclined fibre transmission line being directed towards the end of the said axial fibre transmission line at the interface, with each fibre transmission line terminating at the said gap at the interface, whereby • the said fibre optic transmission lines form at least a continuous optical path between said members during relative rotation. .2. A light-operated slip ring according to claim 1 characterised by bilateral transmission means each member has two fibre transmission lines with each member carrying an inclined fibre transmission line directed to an axial fibre transmission line carried by the other said member. 3. A light-operated slip ring according to preceding claim 1 or 2 characterised in that at. least one of said members carries a plurality of inclined fibre transmission lines directed to an axial transmission line on the other said member said inclined transmission lines being each adapted to receive different chromatic light signals and by dichromatic filter means to separate the signals received and transmitted by the said axial fibre transmission line. 4. A light-operated slip ring according to claim ' 1 characterised in that the said fibre transmission line extends outside of the said first and the said second members, and the said inclined transmission line terminate remotely in a light emitting diode, and the said on-axis transmission line terminates remotely in a detector, 5. A light-operated slip ring according to claim 2 characterised by a blocking filter in the said on-axis transmission line selected to prevent cross- modulation. 6. A light-operated slip ring in which a signal is transmitted through a gap across an interface between a first member and a second member which have relative rotational motion the one to the other about a common axis, characterised by each of said members, carrying at least one inclined off-axis fibre transmission line along which the light is transmitted across a gap formed at the interface between the said two members, and each of the other said members carries an on-axis fibre transmission - line, the said inclined fibre transmission lines being each directed to the end of the said axial fibre transmission line opposite the said gap at the interface, whereby the said fibre optic transmission lines form at least a pair of continuous optical paths between said members during relative rotation. 7. A light-operated slip ring according to preceding claim 6 characterised in that at least one of said members carries a plurality of inclined ' fibre transmission lines directed to an axial transmission line on the other said member, said inclined transmission lines being each adapted to receive different light signals, and by filter means to separate the signals received and transmitted by the said axial fibre transmission lines. 8. A light-operated slip ring according to claim 1 or claim 7 characterised in that the said first member encircles at least part of the said second member and by bearings between the said first and the said second member to allow relative rotation of one about the other, each said members having a face In which the said fibre transmission lines terminate, said faces being spaced apart to form an air-gap acros-s which light from at. least one . inclined fibre transmission line is directed to the said on—axis fibre transmission line. 9. A light-operated slip ring constructed and operating substantially as described and illustrated with reference to FIGS. 1 and 2 or 3 or 4 of the accompanying drawings.

Inventors: MATTHEWS HERBERT GEORGE, MATTHEWS, HERBERT, GEORGE
Applicants: COMMW OF AUSTRALIA, THE COMMONWEALTH OF AUSTRALIA CARE OF THE SECRETAR
Application year: 1984
Main classification: G02B7
IPC codes: G02B6