GB2221031A

GB2221031A - Electrical machine

Info

Publication number: GB2221031A
Application number: GB8914042A
Authority: GB
Inventors: Juergen Maass; Helmut Meyer
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1988-06-21
Filing date: 1989-06-19
Publication date: 1990-01-24
Also published as: DE3820903A1; FR2633114A1; JPH0241648A; GB8914042D0

Description

DESCRIPTION

ELECTRICAL RACHINE 2221031 The invention relates to an electrical machine according to the preamble of the main claim.

Such a machine is known from DE-OS 34 18 153. This machine may be in the form of a motor, for example in the form of a commutatorless directcurrent motor. In order to generate the commutation signals or in order to sense the angular position of the rotor, the rotor contains a signal trace, which is scanned by means of a sensor.

The disadvantage of this kind of signal formation is to be seen in the fact that a sensor that is disposed in the direct vicinity of the rotor is exposed, because of the motor currents, to high electromagnetic interference fields. Furthermore, the sensor may be damaged by the heat from the motor; at the same time, however, the replacement of such a sensor that is located inside a motor is extremely time-consuming.

The object of the invention, therefore, is to create an electrical machine in which the reliable, trouble-free detection of the angular position of the rotor is guaranteed.

The object of the invention is achieved by an apparatus of the kind described by the characterizing features of claim 1.

An essential advantage of the invention is to be seen in the fact that there is no longer any disturbance, t because of motor operation, to the highly sensitive electronic component constituted by the optical sensor. Furthermore, the optical sensor can easily be replaced in the event of a defect. Intervention in the motor is not necessary.

A further advantage is to be seen in the use of optical fibres for the transmission of the optical signals. As is known, optical fibres are virtually insensitive to effects of temperature as well as to electromagnetic interference fields.

In a further development of the invention, it is proposed that the optical sensor be integrated into an electrical control circuit. Such an electrical control circuit is necessary particularly in the case of a direct-current motor in order to energize the individual motor windings and contains the entire control electronics. The integration of the optical sensor has the advantage that the signals from the sensor can be supplied directly to the control circuit without any additional transmission paths. Such control circuits are usually protected against dust and other environmental influences by means of a housing. This means that the optical sensor, too, undergoes the same protection measures.

In a further development of the invention, the optical fibre may be provided with a plug-in connector. This plug-in connector has the task of adapting the end of the optical fibre facing the signal trace in such a manner that it can be plugged into the housing of the motor. For this purpose, a corresponding socket is provided on the housing of the motor. Such a plug-in k 3 connection also has the advantage that the motor can very easily be disconnected from the electrical control circuit, for example if the motor is being replaced or if the control circuit is being replaced or also if the optical fibres themselves are being replaced. It is also possible to design this plug-in connector so that it is suitable for a plurality of optical fibres, with the result that only one single plug-in connector is necessary for a multiplicity of transmission lines.

In a further embodiment of the invention, it is proposed that the optical fibre be provided with a reflex head. This has the advantage that the transmission of the light from the light source to the signal trace is effected via the optical fibre. This light is reflected on the signal trace and the reflected radiation is supplied to the optical sensor likewise by means of the optical fibre. It is practical for the signal trace to be a plastic sheet, which is attached at the end face of the rotor. Reflecting and non-reflecting surface regions are provided on this plastic sheet.

In advantageous manner, the distribution of these surface regions corresponds to the pole pitch of the rotor, i.e. the optical sensor is supplied with a signal shape that is identical with the pole-angle position of the rotor, with the result that the commutation signals for driving the motor can be derived directly from the sensed signals.

The generation of the optical signal is accomplished, for example, by a light-signal generator, which is situated likewise in the electrical control circuit. The light signal is sent by means of a so-called Y- - 4 coupler to the reflex head of the optical fibre. A light-emitting diode may be used as the light-signal generator.

The invention is explained in greater detail in the following on the basis of a specimen embodiment, with reference being made to the drawings, in which:

Fig. 1 shows a schematic representation of an apparatus for the detection of the rotor position; Fig. 2 shows a schematic representation of a rotor with signal trace; Fig. 3 shows a partial view of a motor with a plug-intype optical fibre.

Of a motor, for example a commutatorless direct-current motor, Fig. 1 shows a rotor 1. This rotor 1 bears a plurality of permanent magnets on a shaft 2. These permanent magnets 3 are disposed on the shaft 2 with alternating polarity and radial direction of magnetization in such a manner that the result is a rotor with three pairs of poles. Situated at the end face 4 of the rotor 1 is a signal trace consisting of lightreflecting regions 5a, b, c and non-reflecting regions 6a, b, c. The distribution of the regions is such that they correspond to the pole pitch of the permanent magnets 3. Provided for the sensing of the angular position of the rotor are three optical fibres 7, 8, 9, the ends of which are directed at the signal trace 4. These optical fibres 7, 8, 9 are attached, for example, to the housing of the rotor (not shown here). At their ends facing the signal trace, the optical - 5 fibres 7, 8, 9 comprise ref%lex heads. This means that each optical fibre simultaneously emits a light signal and receives back the light reflected by the signal trace. The optical fibres 7, 8, 9 lead into a housing 10, in which three optical sensors 12, 13, 14 and three light-signal generators 15a, b, c are accommodated on a board 11. This housing additionally contains, for example, an electrical control circuit necessary for the energization of the motor. Each of the optical fibres 7, 8, 9 consists of a multiplicity of thin individual optical fibres, which are grouped together to form a bundle. The light, which is generated by the light signal generators 15a, b, c, is injected via so-called Y- couplers, i.e. of each of the optical fibres 7, 8, 9, some of the individual optical fibres are connected to the light-signal generators 15a, b, c. The other individual optical fibres are connected to the respective optical sensors 12, 13, 14. Consequently, the light is transmitted to the reflex head of the respective optical fibre by means of some of the individual optical fibres. The other individual optical fibres transmit the light reflected on the signal trace 4 to the respective optical sensors. The received by the optical sensors 12, 13, 14 can be used both for determining the rotational speed of the rotor 1 and also for determining its angular position. The detection of the angular position of the rotor is necessary, for example, for the commutatorless energization of the motor coils. It becomes apparent from Fig. 1 that no electronic components are disposed on the rotor or, thus, in the immediate vicinity of the magnetic fields of the permanent magnets or of the motor coils (not shown here). All components, such as sensors, light sources, are situated outside the motor in the housing 10. Damage to these electronic components because of interference fields, vibrations or effects of temperature is, therefore, impossible.

Fig. 2 shows, in a schematic representation, a further variant of a rotor with signal trace. The construction of the rotor 16 is identical with that of the rotor shown in Fig. 1. Merely the signal trace 17 exhibits a slightly modified form. This signal trace 17 comprises three individual traces 18, 19, 20. Each of these individual traces is assigned an optical fibre 21, 22, 23. These optical fibres 21, 22, 23 are juxtaposed in the radial direction and can, therefore, be combined in space-saving manner in one single housing 24. The optical fibres 21, 22, 23 lead likewise to a housing (not shown here), in which are accommodated the optical sensors and a light-signal generator.

The schematic representation shown in Fig. 2 is reproduced in Fig. 3 in a partial view of a motor in sectional representation. The rotor 16 is rotatably held in a motor housing 27 via a shaft 25 and via ball bearings 26. Situated on the motor housing 27 are appropriate motor coils 28, 29, which form the stator of the motor. Provided in the motor housing 27 is a recess 30, in which is situated the housing 24 of the optical fibres 21, 22, 23. The housing 24 is occupied by a disconnectable plug-in connector, which is mounted in the recess 30, with the result that it is easy both for the optical fibres to be mounted on the motor and also for the optical fibres to be replaced. The optical fibres 21, 22, 23 comprise the reflex heads 31, 32, 33, which face a signal trace 17. This signal trace 17 is attached on the rotor 16 and comprises the individual traces 18, 19, 20 described in Fig. 2. Of course, instead of the three optical fibres shown in the description, it is also possible for there to be a plurality of optical fibres. The grouping-t6gether of the motor- facing ends of the optical fibres in one housing 24 is advantageous in any case, because this common housing considerably facilitates the installation and the replacement of the entire optical-fibre bundle.

It will be understood that the Invention has been described above purely by way of example, and that various modifications of detail can be made within the ambit of the invention.

LIST OF REFERENCE CHARACTERS 1 2 3 4 sa 5b SC 6a 6b 6C 7 Optical fibre a Optical fibre 9 Optical fibre Housing (for optical senSors etc.) 11 Board 12 Optical sensor 13 optical sensor 14 optical sensor isa Light-signal generator 15b Light-signal generator isc Light-signal generator 16 Rotor Signal trace Individual trace Individual trace Individual trace Rotor Shaf t Permanent magnet Signal trace Surface region Surface region Surface region Surface region Surface region Surface region 17 is 19 21 Optical fibre 22 Optical fibre 23 Optical fibre 24 Housing (plug-in connector) Shaft 1 26 27 28 29 30 31 32 33 Ball bearing Motor housing Motor coil Motor coil Recess Reflex head Reflex head Reflex head

Claims

1. An electrical machine comprising a stator and a rotor and a housing therefor, the rotor being provided with one or more optically detectable signal traces for the sensing of the angular position of the rotor, and one or more optical sensors also being provided, wherein the one or more optical sensors are disposed outside the said housing of the electrical machine, and one or more optical fibres are provided for the transmission of optical signals between the region of the one or more signal traces and the one or more optical sensors.

2. An electrical machine according to claim 1, wherein an electrical control circuit is provided outside the said housing, and the one or more optical sensors are incorporated in the control circuit.

3. An electrical machine according to claim 2, wherein the one or more optical fibres are provided, at the end facing the one or more signal traces, with a plug-in connector, and the saidhousing has a recess complementary therewith for the separable connection of the one or-more optical fibres to the said housing.

4. An electrical machine according to claim 3, wherein a plurality of optical fibres are employed but these jointly terminate in a single plugin connector.

11 -

5. An electrical machine according to any of clairs 1 to 4, wherein the one or more optical fibres are provided with a reflex head at the end facing the signal trace.

6. An electrical machine according to any of claims 1 to 5, wherein the one or more signal traces are constituted by a plastics sheet, said plastics sheet being attached at an end face of the rotor, and the optical signals being produced with the aid of surface regions having different characteristics of reflection.

7. An electrical machine according to claim 6, wherein the distribution of the surface regions having different characteristics of reflection corresponds to the pole pitch of the rotor (the angular distribution of the pole of the rotor).

8. An electrical machine according to any of claims 1 to 7, wherein a light-signal generator is included in the electrical control circuit, which (in use) generates a light signal which i fed into the one or more optical fibres.

9. An electrical machine according to claim 1, substantially as described with reference to any Figure or Figures of the accompanying drawings.

Published 1990 at The Patent Office, State House. 66'71 ILghHolborn, LondonWClR4TP.Purther copies maybe obtainedfrom The Patent Office. Sales Bpanch. St Mary Cray. Orpington, Kent ERS 3RD Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1'87