GB2115139A

GB2115139A - Remote monitoring of the position of a member

Info

Publication number: GB2115139A
Application number: GB08203911A
Authority: GB
Inventors: David Glyndwr White
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1982-02-10
Filing date: 1982-02-10
Publication date: 1983-09-01
Also published as: GB2115139B

Abstract

To avoid electrical disturbances and fire risks which may occur when electrical position sensors are used, the position of the member is determined using the movement of a spatial distribution of radiation of different wavelengths in response to movement of the member. The radiation is provided by a broad band source such as an array of LEDs 2 and is transmitted along a common optical fibre 4 to the location of a shaft 6. A diffraction grating 7, attached to the shaft 6 to move with it, produces a spatial distribution of radiation of different wavelengths which is collected by an output fibre 10, the wavelength picked up depending on the position of the grating 7, hence the position of the shaft 6 can be determined. Signals front spectrometer 11 comprising a diffraction grating 14 and a CCD array 15 are sent to a controller 17 where they are compared with desired position signals for control of the position of the shaft 6 by means of hydraulic line 18. <IMAGE>

Description

SPECIFICATION Apparatus for generating and transmitting information concerning the position of a member This invention relates to apparatus for generating and transmitting information concerning the position of a member.

In many circumstances it is undesirable to employ electrical circuits since they are vulnerable to electrical, magnetic or electromagnetic disturbances and may also present a fire risk.

The position of a rotating member can be monitored using a conventionai optical disc encoder but this may be difficult to accommodate because a number of input and output lines are required and it must also be accurately set up.

This invention arose in an effort to provide apparatus which is of simple design, has few input and output lines and which employs electromagnetic radiation to carry positional information.

Accordingly, this invention provides apparatus for generating and transmitting information concerning the position of a member comprising means for providing a spatial distribution of radiation, having different wavelengths at different parts of the distribution, adjacent one end of an optical fibre, and means for moving the spatial distribution relative to the said one end in response to movement of the member so that the wavelength of radiation transmitted from the one end to another end of the optical fibre represents the position of the member.

The radiation may be produced by a source or sources with a wide range of wavelengths, such as an array of LEDs or a white light source.

The spatial distribution of the radiation obtained may be provided by passing radiation from a single source through a prism or by using a diffraction grating. It may alternatively be directly provided from different sources which produce respective different wavelengths.

The member may be one which undergoes rotational and/or linear motion.

In one embodiment of the invention the member rotates and the end of the optical fibre is fixed and receives the spatial distribution of radiation which is arranged to move as the member rotates. In another embodiment of the invention the member undergoes linear motion and the spatial distribution does not move, the optical fibre which receives the radiation moving with the member. Hence in both cases the relative position of the spatial distribution and the optical fibre vary in accordance with the movement of the member. It is preferable that, over the range of motion studies, there is a one to one relationship between the wavelength of radiation collected by the optical fibre from the spatial distribution and the position of the member. Hence by decoding the information received the position of the member can be determined.Thus by employing this invention it is possible to provide an optical system which is of simple design and only requires one input and one output line.

The invention is further described by way of example with reference to the accompanying drawing in which the Figure schematically illustrates apparatus constructed in accordance with the invention.

At a region defined by the broken line 1 there is located an array of three LEDs 2A, 2B, 2C and an associated electrical system, not shown, for driving them. The LEDs 2A, 2B and 2C emit radiation of respective different wavelengths. Radiation from each LED 2 is transmitted along one of a number of optical fibres 2' capable of transmitting the aforementioned wavelengths. The optical fibres 2' are coupled via a mixing rod 3 to a common optical fibre 4. The radiation is transmitted along the common optical fibre 4 to a region indicated by a broken line 5, remote from the region 1, where a shaft 6 is located. The shaft 6 rotates through a limited angle and it is this angle which it is desired to monitor and control.A reflective diffraction grating 7 is mounted to move with the shaft 6 and, together with a lens 8, they are contained within a housing 9, which shields them from external radiation. One end of the common optical fibre 4 is fixed by the housing 9 at the focal plane of the lens 8, which directs the radiation from the common optical fibre 4 onto the diffraction grating 7.

The radiation incident on the diffraction grating 7 is a homogenous mixture of the three different wavelengths from the LED sources 2A, 2B and 2C which are diffracted through three respective different angles. Thus the three different wavelengths are focussed by the lens 8 at respective different points A, B and C in the focal plane of the lens 8 when the grating is in the illustrated position. Accordingly the grating 7 and the lens 8 consitute means for providing a spatial distribution of different wavelengths of radiation at the focal plane.

An optical output fibre 10 lies in the focal plane of the lens 8 at the point B and is spaced from the common optical fibre 4.

When the diffraction grating 7 is in the position shown in the diagram the wavelength collected by the output fibre 10 at the point B is that emitted by LED 2B. If the shaft 6, and hence the diffraction grating 7, rotates clockwise or anticlockwise the spatial distribution moves so that the radiation from 2C or 2A respectively is focussed on the end of the fibre 10. Thus there is a relationship between the wavelength focussed at the point B and collected by the output fibre 10, and the position of the shaft 6.

The diffracted radiation collected by the output fibre 10 is then transmitted along it to a detecting spectrometer 11 which is in the region 1 and which determines the wavelength of radiation carried by the output fibre 10. The detecting spectrometer 11 comprises a spectrometer housing 12 similar to the housing 9, a spectrometer lens 13, a reflective spectrometer diffraction grating 14 and a charge coupled device (CCD) detector array 15. Radiation from the output fibre 10 enters the spectrometer housing 12 at a fixed point in the focal plane of the spectrometer lens 13 which directs the radiation onto the spectrometer grating 14 which is fixed.The radiation is reflected and diffracted by an amount depending on wavelengths and passes again through the spectrometer lens 13 which focusses it onto the CCD array 15, which also lies in the focal plane of the spectrometer lens 13. Thus the position of the CCD array 15 where the radiation is detected gives the wavelength transmitted. Therefore by detecting the wavelength of radiation which passes along the fibre 10 the position of the shaft 6 is determined.

Electric signals representative of the wavelength of radiation are generated at the CCD array 15 and are sent via a conductor 16 to an electronic drive unit 17. An operator enters into the unit 17 the desired position of the shaft 6 and the unit 17 compares this with the actual position as indicated by the signal on line 16. The result of this comparison is used to control the pressure in a hydraulic line 18. This hydraulic pressure operates a shaft driving unit 6A so as to move the shaft 6 in a direction towards the desired position.

Claims

1. Apparatus for generating and transmitting information concerning the position of a member comprising means for providing a spatial distribution of radiation, having different wavelengths at different parts of the distribution, adjacent one end of an optical fibre; and means for moving the spatial distribution relative to the said one end in response to movement of the member so that the wavelength of radiation transmitted from the one end to another end of the optical fibre represents the position of the member.

2. Apparatus as claimed in claim 1 and wherein the said means for providing a spatial distribution comprises a first diffraction grating arranged to separate different frequency components from a beam of radiation containing said components.

3. Apparatus as claimed in claim 2 and wherein the said first diffraction grating is reflective.

4. Apparatus as claimed in claim 2 or 3 and wherein the said first diffraction grating is attached to move with the member.

5. Apparatus as claimed in claim 2 or 3 and wherein the optical fibre is attached to move with the member.

6. Apparatus as claimed in any preceding claim including means for determining the wavelength or radiation transmitted along the optical fibre.

7. Apparatus as claimed in claim 6 and wherein the said means for determining the wavelength includes a second diffraction grating.

8. Apparatus as claimed in claim 6 or 7 and including a CCD array for detecting the radiation.

9. Apparatus as claimed in any preceding claim and including a LED array to provide a radiation source.

10. Apparatus substantially as illustrated in and described with reference to the accompanying drawing.