Apparatus and method for detecting movement of an object

The movement of a body (1) is determined by mounting on or in the body one or more sources (3,4) and one or more detectors (12,14) such that each source propagates polychromatic light along a path to a detector. Radiation modulation means (19;25) is supported by the body such that a change in the movement of the body causes a displacement of the radiation modulation means in at least one light path to vary the distributed spectral content of the light reaching the detector. The or each detector is adapted to detect the intensity of incident radiation at a plurality of different wavelengths, and analysis means (18) interprets the output of each detector in terms of the movement of the body.

This invention relates to apparatus for determining movement. The need for 
equipment capable of determining movement arises in a large number of 
situations such as navigation systems, stabilizers etc, and is usually 
fulfilled by means of a gyroscope. A conventional gyroscope is in the form 
of a rapidly spinning wheel set in a framework such that it is free to 
tilt in any direction. The wheel retains its original orientation 
regardless of the subsequent movement of the vehicle etc on which it is 
mounted. It therefore acts as a direction indicator from which the 
movement/direction of the vehicle can be established. 
Conventional gyroscopes have several intrinsic disadvantages. The 
requirement for a rapidly spinning wheel makes them mechanically 
complicated, and difficult to set up. In addition the rotation of the 
wheel must be maintained, thereby requiring a driving force such as a 
motor or air jets. 
It is an object of the present invention to provide an apparatus for the 
accurate determination of movement, which avoids the problems associated 
with the spinning wheel of a conventional gyroscope. 
Accordingly there is provided apparatus for determining movement comprising 
a body, there being mounted on or in the body one or more sources and one 
or more detectors, the or each source being each adapted to propagate 
polychromatic light along a path to a detector, the or each detector being 
adapted to detect the intensity of incident radiation at a plurality of 
different wavelengths, and radiation modulation means supported by the 
body such that a change in the movement of the body in at least one 
direction causes a displacement of the radiation modulation means in the 
said path such as to vary the distributed spectral content of the light 
reaching the one or more detectors. 
The change in the movement of the body detected by the apparatus may be 
movement applied to a body from a stationary position. The apparatus is 
therefore capable of acting as a vibration detector. Alternatively the 
change in the movement of the body may be a change in the velocity of the 
moving body, or a change in the direction of movement thereof. The 
apparatus is therefore additionally capable of acting as an accelerometer 
or a direction indicator, and can perform all the functions of a 
conventional, spinning wheel gyroscope. 
The apparatus preferably includes means for analysing the variation in the 
distributed spectral content to determine the change in the movement of 
the body. Typically this is carried out by monitoring the ratio of 
intensities at two separate wavelengths of the light. In a preferred 
alternative, the one or more detectors each comprise at least first and 
second photo-responsive elements, the responsivity with respect to 
wavelength of the first element being different from that of the second, 
signals from the photo-responsive elements being fed to the analysis means 
which calculates, from the signals from the photo-responsive elements, the 
colour of the radiation incident on the one or more detectors as 
represented by two or more parameters on the Chromaticity (CIE) Diagram. 
In one convenient arrangement two different photo-responsive elements are 
employed, each with its own wavelength responsivity characteristic. 
Alternatively, one or both of the photo-responsive elements includes a 
coloured filter to impart a colour response characteristic, thereby 
allowing two identical photo-responsive elements to be employed, if 
desired. Preferably the responsivity with respect to wavelength of the at 
least first and second photo-responsive elements are such that their 
respective wavelength/intensity curves overlap for at least a part of the 
wavelength spectrum. 
By employing at least first and second photo-responsive elements, a change 
in colour is determined by assessing the change in the whole of a selected 
part of the spectrum (colour modulation), as opposed to merely detecting 
the change at one or more selected wavelengths (wavelength modulation). 
Thus a change from colour A (represented by wavelength/intensity curve A) 
to colour B (represented by wavelength/intensity curve B) will be 
calculated from the area between the two curves, thereby giving a more 
complete analysis of "true" colour. Wavelength modulation, whilst giving 
an indication of the change, is limited in that it is a calculation based 
on the distance between the curves at selected wavelengths. Whichever 
method is employed, the monitored variation in the distributed spectral 
content is compared with calibrated measurements of the variations for 
different degrees and directions of movement of the body. 
By the term `polychromatic light` there is herein meant any 
multi-wavelength radiation, and is specifically meant to include both 
visible light and infra red radiation. The term `colour`, whilst used 
herein for ease of understanding, should in no way imply that only visible 
light may be employed. Where the apparatus employs a source emitting 
radiation outside of the visible spectrum, the term `colour` will refer to 
the spectral distribution of the radiation. 
There is conveniently mounted on or in the body at least two pairs of 
sources and detectors, each pair defining a polychromatic light path, the 
paths of at least two pairs being in different directions, the arrangement 
being such that a change in the movement of the body in either of at least 
two directions causes a displacement of the radiation modulation means in 
the path of at least one of the pairs of sources and detectors such as to 
vary the distributed spectral content of the light reaching the or each 
detector. With this arrangement, movement in two dimensions can be 
determined, the apparatus being capable of detecting movement in any 
direction in a predetermined plane. Conveniently the at least two pairs of 
sources and detectors are arranged such that the light path of each is in 
the same plane. 
There is preferably provided at least three pairs of sources and detectors, 
each pair defining a polychromatic light path, the arrangement being such 
that a change in the movement of the body in any direction causes a 
displacement of the radiation modulation means in the path of at least one 
of the pairs of sources and detectors, such as to vary the distributed 
spectral content of the light reaching one or more of the detectors. 
Preferably, the paths of the at least three pairs are in different 
directions and the light path of the third pair is in a plane at an angle 
.theta. to that or those of the other two pairs (where .theta..noteq.0), 
such an arrangement allows the detection of movement in three dimensions. 
Conceivably the radiation modulation means and the pairs of sources and 
detectors are such that a change in the movement of the body in any 
direction causes a displacement of the radiation modulation means in the 
path of at least two of the pairs of sources and detectors such as to vary 
the distributed spectral content of the light reaching two or more of the 
detectors. 
Preferably the radiation modulation means and the pairs of sources and 
detectors are such that a change in the movement of the body in any 
direction causes a displacement of the radiation modulation means such as 
to produce a distributed spectral content of the light reaching the 
detectors which is unique for that direction of movement. The analysis 
means is therefore able to determine, from any particular combination of 
signals from the detectors, a single unambiguous value for both magnitude 
and direction of movement. 
The radiation modulation means preferably comprises one or more filter 
elements which attenuate different wavelengths of light to a differing 
extent. Movement of the body causes a corresponding movement of the one or 
more filter elements thereby modulating the "colour" of the radiation 
reaching the one or more detectors. Analysis of the colour modulation can 
be used to determine the movement of the body. In one convenient 
arrangement the one or more filter elements comprise one or more coloured, 
transparent spheres, typically so-called ruby spheres. These spheres not 
only modulate the radiation but in addition help to focus it on to the one 
or more detectors, thereby providing a sharper resolution for the more 
accurate detection of very small amounts of movement. 
The one or more spheres are conceivably suspended by means of one or more 
flexible elongate elements secured to the body. The one or more flexible 
elongate elements may be wires or elastic elements, and enable the one or 
more spheres to be mounted on the body in such a way as to allow movement 
with respect thereto in all three dimensions. Alternatively the one or 
more spheres are suspended by means of a plurality of jets of fluid, 
typically air, eminating from nozzles mounted on the body. 
In an alternative arrangement the one or more filter elements comprise, or 
are mounted on, longitudinally extending members. Conveniently at least 
one of the one or more filter elements comprises an optical fibre. 
Alternatively or additionally at least one of the one or more filter 
elements comprises a filter strip, or comprises a coloured, transparent 
sphere mounted on a longitudinally extending member. 
In one convenient arrangement at least one of the one or more 
longitudinally extending members is in the form of a cantilevered beam, 
secured to the body at or towards one or its ends with its other end free 
to move laterally of its longitudinal access. Movement of the body causes 
the free end of the cantilever beam to vibrate, producing a displacement 
of the radiation modulation means in the path of one or more pairs of 
sources and detectors. Alternatively one of the one or more longitudinally 
extending members is in the form of a cross-beam secured to the body at or 
towards both of its ends with its central portion free to move laterally 
of its longitudinal access. In another arrangement at least one of the one 
or more longitudinally extending members is suspended as described 
previously by means of one or more flexible elongate elements secured to 
the body. 
Where the one or more filter elements comprise, or are mounted on, 
longitudinally extending members, movement of the body in the direction of 
the longitudinal axis of one of the filter elements may not result in a 
displacement of that filter element in the path of its pair of sources and 
detectors. Even where such a displacement does occur it may not result in 
a modulation of the light reaching the detector. Accordingly in such a 
case, the radiation modulation means conveniently comprises at least first 
and second filter elements each comprising, or mounted on, a 
longitudinally extending member, the longitudinal axis of the first filter 
element being in a different plane from that of the second filter element, 
the arrangement being such that a change in the movement of the body in at 
least one direction causes a displacement of the second filter element in 
the path of the third pair of sources and detectors, and a change in the 
movement of the body in another direction causes a displacement of the 
first filter element in the path of one or both of the first and second 
pairs of sources and detectors. By providing two filter elements with 
their longitudinal axes in different planes, even if the movement of the 
body is in the direction of the longitudinal axis of one of the filter 
elements, it will at least be transverse to the longitudinal axis of the 
other filter element. 
The one or more sources are preferably adapted to produce a white light 
signal. The invention further resides in a method of determining movement 
employing apparatus as hereinbefore described. In particular, a method of 
determining a change of movement of a body comprises propagating 
polychromatic light along at least one light path to one or more 
detectors, supporting radiation modulation means such that a change in the 
movement of the body in at least one direction causes a displacement of 
the radiation modulation means in at least one light path such as to vary 
the distributed spectral content of the light reaching the or each 
detector, and calculating the change of movement of the body from the 
variation in the distributed spectral content of the light reaching the or 
each detector.

Referring to FIGS. 1 and 2, there is shown a body in the form of a housing 
1, being generally square in cross-section and having a circular aperture 
2 extending longitudinally through its centre. Mounted on the housing 1 
are two light sources 3 and 4, each source being received in a recess 5 
which is present in the upper face 6 of the housing. Adjacent the source 3 
is an optical fibre 7 which transmits light from the source 3 to the 
region of the aperture 2. On the opposite side of the aperture 2 is 
another optical fibre 9, in alignment with the fibre 7 and spaced 
therefrom to leave a gap 11. At the end of the fibre 9 remote from the gap 
11 is a detector in the form of a charge coupled device (CCD) array 12, 
the array 12 being received in a corresponding recess 13 in the housing 1. 
In similar manner optical fibres 8 and 10 transmit light from the source 
4, across the gap 11 and to a CCD array 14 received in a recess 15 in the 
housing. Arrays 12 and 14 are in communication via lines 16 and 17 with a 
microprocessor 18, shown in FIG. 1 to be external to the housing 1 but 
which may equally be mounted directly thereon. 
A cantilevered optical fibre 19 is present in the gap 11, the longitudinal 
axis of the cantilevered fibre 19 being orthogonal to those of the fibres 
7 and 9, and 8 and 10. The cantilevered fibre 19 is secured at its lower 
end 20 in a U-shaped support 21. The support 21 is mounted in a base plate 
22, the base plate acting as a closure for the aperture 2 and as a 
mechanical linkage between the body 1 and the lower end 20 of the 
cantilevered fibre 19. In the event of flexing of the cantilever fibre 19 
the upper end 23 thereof is free to move in the gap 11. 
The operation of the device of FIGS. 1 and 2 will now be described. 
Polychromatic light from the source 3, is transmitted to the array 12 
along a first light path constituted by the optical fibres 7 and 9, the 
light path extending across the gap 11 and through the cantilevered fibre 
19. Similarly light from the source 4 travels along a second light path 
constituted by optical fibres 8 and 10, also including the gap 11 and 
cantilevered fibre 19. The light passing through the cantilevered fibre 19 
undergoes colour modulation in that the spectral content of the light is 
changed by the attenuation of some wavelengths to a greater or lesser 
degree than the attenuation of others. Incident light is detected by the 
arrays 12 and 14 and signals are passed to the microprocessor 18 which 
calculates the intensity of light of selected wavelengths received by the 
arrays. Microprocessor 18 determines a factor of the wavelength modulation 
such as the ratio of the intensities of light received at two different 
wavelengths. 
A change in the movement of the body 1, whether due to a vibration applied 
thereto, a change in the velocity of the body, or a change in the 
direction of the movement thereof, causes a flexing of the cantilevered 
fibre 19. A component of movement in the X-direction, as shown in FIG. 1 
causes the upper end 23 of the cantilevered fibre to move laterally of the 
light path between optical fibres 8 and 10. Similarly a component of 
movement in the Y-direction causes the upper end 23 to move laterally of 
the light path between optical fibres 7 and 9. Movement of the cantilever 
fibre in one or both of the light paths varies the colour modulation of 
the light reaching the CCD arrays. The microprocessor 18 monitors the 
change in the factor of the wavelength modulation and compares this with 
predetermined calibrated values for known changes of movement. In this way 
the change in wavelength modulation is interpreted as a calculation of the 
movement of the housing 1. The device of FIGS. 1 and 2 is therefore 
capable of detecting any change of movement in the plane containing the X 
and Y directions. 
A component of movement in the Z-direction will not produce flexing of the 
cantilever fibre 19 and hence will not be detected. If it is desired to 
monitor movement in three dimensions, the device such as that of FIG. 3 
may be employed. The device of FIG. 3 is based on that of FIG. 1, and 
similar components are designated with a like reference numerals. The 
housing 1 and associated elements are enhanced by the provision of an 
additional housing 1', together with a cantilevered optical fibre 19', 
rotated through 90.degree. with respect thereto. This means that the 
longitudinal access of the cantilever fibre 19' lies along the axis of the 
X-direction, as opposed to the Z-direction as does the cantilever fibre 
19. Therefore any component of movement in the Z-direction applied to the 
housings 1 and 1', which are secured for movement one to the other, will 
produce a flexing of the cantilevered fibre 19' so that it moves laterally 
of the light path between optical fibres 8' and 10'. The light path 
between optical fibres 7' and 9', the presence of which is not strictly 
essential, serves as a corroboration to the movement in the Y-direction 
detected by the light path between optical fibres 7 and 9. With the 
arrangement of FIG. 3, a change of movement in any direction will produce 
a flexing of at least one of the fibres 19 and 19', which flexing can be 
analysed by the microprocessor 18 to calculate the extent and/or direction 
of the movement. 
FIGS. 4 to 6 show embodiments of the invention in which the cantilevered 
optical fibre is replaced by a ruby sphere 25. The ruby sphere, like the 
optical fibre, serves to focus the light from the sources so as to 
increase the sensitivity of the apparatus. Additionally, as the sphere 
performs colour modulation on light passed therethrough in any direction, 
suitable mounting of the sphere allowing movement in three dimensions 
permits the calculation of movement in any direction from a single sphere, 
rather than requiring two optical elements as in FIG. 3. 
FIG. 4 shows the mounting of the ruby sphere 25 by means of a cantilever 
wire 26. The wire is secured to the body 1 at one of its ends and sphere 
25 is secured at the other. Three pairs of optical fibres, 27 and 28, 29 
and 30, and 31 and 32, provide three light paths through the sphere 25, in 
three mutually perpendicular directions. The wire 26 is arched to allow 
fibres access to the sphere. A change in the movement of the housing 1 
causes the sphere 25 to be displaced in one or more of the light paths 
between the optical fibres. As before this displacement results in colour 
modulation of the light signals, which can be used to calculate the 
movement of the housing. 
FIG. 5 shows an arrangement in which the ruby sphere 25 is supported by 
means of air jets eminating from nozzles 33. This again allows 
unrestricted access to the sphere, yet leaving it free to be displaced in 
any direction. 
FIG. 6 shows the ruby sphere 25 suspended by means of flexible elements 
such as wires 34. The wires are attached to the sphere in such a manner as 
to permit movement in any direction, whilst allowing an unobstructed 
passage through the sphere for the light paths from the optical fibres 27 
to 32. 
It will be appreciated that modifications to the aforementioned apparatus 
may be made without departing the scope of the present invention. For 
example, the focusing effect of a ruby sphere may enable calculations of 
movement in three dimensions to be made without the need for three pairs 
of sources and detectors, movement longitudinally along a light path 
resulting in colour modulation due to the change in focus of the 
transmitted beam. Another modification, appropriate where vibration of a 
predetermined frequency is to be detected, is to mount the radiation 
modulation means on a member such as a diaphragm, the natural resonant 
frequency of the diaphragm being that of the predetermined frequency to be 
detected. Vibration at the predetermined frequency results in a much 
greater displacement of the radiation modulation means than vibration at 
other frequencies. These and other modifications will be apparent to those 
skilled in the art as available alternatives, each in accordance with the 
present invention.