Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1989-07-20
1991-09-03
Evans, F. L.
Optics: measuring and testing
By polarized light examination
With light attenuation
356138, 356152, G01B 1100
Patent
active
050447513
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a light source for an optical sensor and an optical measuring device using same.
The general field of the present invention is that of measuring the position of a body, in particular the angular position of a body relative to a frame of reference, in practice a reference plane, the position being measured by means of the relative position or positions of light spots from the source on a linear sensing member.
There is known, in particular from French Pat. No. 76.25996, a light source suitable for use in an optical sensor of the kind briefly described hereinabove.
The light source described in this document is V-shaped. An image of the source is directed, by means of an optical system, for example, onto a linear sensing member, usually in the form of a CCD strip (CCD signifies Charge-Coupled Device and a CCD strip is a strip of charge-transfer photosensitive devices; the expression "CCD strip" is used hereinafter with this sense). The strip is disposed perpendicular to the axis of symmetry of the image of the V-shaped light source. The strip senses the position of light spots which are in fact the intersection of the image of the branches of the luminous V with the strip.
In practice the following arrangements may be used:
the source may be fixed relative to the frame of reference and the strip mounted on the object whose angular position is to be measured;
the source may be mounted on the object whose angular position is to be measured and the strip fixed relative to the frame of reference;
the strip and the source may be mounted on the object whose angular position is to be measured and associated with a mirror fixed relative to the frame of reference or the strip and the source may be fixed relative to the frame of reference and associated with a mirror mounted on the object whose angular position is to be measured.
In all cases the relative position of the light spots mentioned hereinabove on the strip gives the following information:
the distance between them on the strip is a measure of the angle of rotation of the object about an axis parallel to that of the strip,
the "centre of mass" between the two light spots is a measure of the rotation of the object about an axis perpendicular to that of the strip.
In some applications these sources and the measuring devices in which they are used have disadvantages.
The applicant has attempted to use sources of this kind with precision optics disposed between the source and the linear sensing member. In some applications, and in particular those with respect to which the applicant has undertaken the research work which has led to the present invention, there is a simultaneous requirement for highly precise measurement and a large amplitude of the angular scale measured. In practice this leads to the use of a relatively high V-shaped light source and consequently the use of one or more optical systems having a particularly large angular field, the size of the field being related to the diameter of the circle passing through the point of the V and the opposite ends of its branches.
As is well known, the cost of an optical system increases with its angular field.
On the one hand, for economic reasons related to the cost of such optical systems the applicant has realised that it is desirable to have a light source enabling measurement of the angular position of an object relative to a reference plane by means of a linear sensing member with the field of the optical system used minimised or at least optimised.
On the other hand, the applicant has noticed that in some applications it is desirable to reduce at least one of the dimensions of the light source so as to reduce its overall size. This advantage is particularly beneficial when using light sources and optical sensors of the aforementioned type in artificial satellites where any saving of space results in a non-negligible economic saving.
The present invention is particularly directed to a source which:
either can be of equivalent size to the prior art source and adapted to be u
REFERENCES:
patent: 3197643 (1965-07-01), Morris
patent: 4330212 (1982-05-01), Miller
patent: 4869591 (1989-09-01), MacGregor
Hooker, IBM Technical Disclosure Bulletin, vol. 19, No. 9, Feb. 1977, pp. 3349-3350.
Cerutti-Maori Guy
Singer Christian
Evans F. L.
Societe Nationale Industrielle et Aerospatiale
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