Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-11-15
2001-06-19
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C356S028000
Reexamination Certificate
active
06248994
ABSTRACT:
1. BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for determining angular displacement of one or more parts of an object, said method comprising directing at least one beam of electromagnetic radiation towards one or more parts of the object, detecting speckles from the object surface in at least one first image sensor, and determining one or more speckle displacements before and after the angular displacements of said one or more parts of the object as a function of the angular displacements.
The invention also relates to a method of determining twist of a rotating shaft subjected to a load; a method of simultaneously determining angular displacements and surface translations of one or more parts of an object; and a method of determining the radius of angular displacement of an object.
1. The Technical Field
Generally, determination of angular displacement of an object using speckle displacement comprises illumination of the surface of the object by a laser beam. The reflected laser beam generates a speckle pattern which is detected in a linear image sensor. After angular displacement of the object, the displaced speckle pattern is detected in the linear image sensor. The two speckle patterns are then cross-correlated to determine the angular displacement which is provided by the displacement giving maximum cross-correlation.
A drawback of this method is that the determination of the angular displacement depends on the distance from the linear sensor to the object, movements of the object, the radius of displacement, as well as the shape of the object.
2. Prior Art Disclosures
Hayashi and Kitagawa, “High Resolution Rotation-Angle Measurement of a Cylinder Using Speckle Displacement”, Applied Optics, Vol. 22, 1983, p. 3520-3525, disclose a method for measuring the rotation angle of a cylinder, particularly a small rotation angle with high resolution based on the speckle displacement detection in the (near) diffraction field caused by rotation of the cylinder surface. The light intensity distributions of speckles before and after the cylinder surface displacement are detected by a detector array, and displacement of the speckle pattern is measured by computing their cross-correlation function.
Yamaguchi and Fujita, “Laser Speckle Rotary Encoder”, Applied Optics, Vol. 28, No. 20, 1989, p. 4401-4406, disclose a method and apparatus for measuring small rotation angles of a cylinder by detecting displacement of the speckles which appears in the diffraction field of the surface illuminated by a narrow laser beam. The speckle pattern is detected by a linear sensor whose output is cross-correlated before and after the rotation of the cylinder. A resolution of 2 millidegrees is reported.
In both of these prior art techniques, the angular displacement measurement is dependent of the distance of the linear sensor to the cylinder being measured, longitudinal and transversal movements of the cylinder, its radius, and the shape of the object.
2. DISCLOSURE OF THE INVENTION
Object of the Invention
In an aspect, it is an object of the present invention to provide an improved method and apparatus for determining angular displacements of one or more parts of an object.
It is a further object of the present invention to provide such a method and apparatus for which the angular displacement determination is independent of the distance to the object, any longitudinal and transversal movements of the object, the shape of the object, and the radius of angular displacement.
In another aspect, it is the object of the present invention to provide a method and apparatus for determining twist of an object, in particular for determining twist of a rotating object, e.g. a driving shaft, under load.
In still another aspect, it is the object of the present invention to provide a method and apparatus for determining both angular displacement and surface translation of one or more parts of an object, in particular for determining the radius of angular displacement thereof.
Further objects will appear from the description of the invention and its preferred embodiments.
Solution According to the Invention
According to an aspect of the invention, there is provided a method for determining angular displacements of one or more parts of an object, said method comprising
a) directing at least one beam of substantially coherent and substantially parallel electromagnetic radiation towards said one or more parts of the object positioned in a first position;
b) detecting in at least one first image sensor first one or more distributions of speckles provided by at least a part of the electromagnetic radiation scattered from said one or more parts of the object in said first position;
c) angular displacing (&thgr;,&phgr;) said one or more parts of the object in a second position;
d) detecting in said at least one first image sensor second one or more distributions of speckles provided by at least a part of the electromagnetic radiation scattered from said angularly displaced one or more parts of the object in said second position; and
e) determining one or more displacements (&Dgr;x, &Dgr;y) of the first and second detected distributions of the speckles as a function of the angular displacements of said one of more parts of the object between said first and second positions;
wherein
f) the at least a part of electromagnetic radiation scattered from said one or more parts of the object is Fourier transformed by at least one Fourier-transforming means having a Fourier plane, and
g) the at least one image sensor is being positioned in a detector plane in or near said Fourier plane of said at least one Fourier-transforming means.
According to another aspect, there is provided an apparatus for determining angular displacements of one or more parts of an object; said apparatus comprising:
a) means for directing at least one beam of substantially coherent and substantially parallel electromagnetic radiation towards said one or more parts of the object;
b) at least one first image sensor for detecting first and second one or more distributions of speckles provided by at least a part of the electromagnetic radiation scattered from said one or more parts of the object before and after they are being angularly displaced;
c) means for determining displacements of the detected first and second one or more distributions of speckles as a function of the angular displacements of said one or more parts of the object;
d) means for Fourier-transforming at least a part of the electromagnetic radiation scattered from said one or more parts of the object; said means having a Fourier plane in or near the plane of the detecting means of the first and second one or more distributions of speckles.
It has surprisingly turned out that if
(f) at least a part of the electromagnetic radiation scattered from said one or more parts of the object is Fourier transformed by a least one Fourier-transforming means having a Fourier plane, and that if
(g) at least one image sensor is being positioned in a detector plane in or near said Fourier plane of said at least one Fourier-transforming means,
it is obtained that determination of the angular displacement is independent of
the distance to the object,
any longitudinal and transversal movements of the object,
the wavelength of the source,
the shape of the object, and
the radius of angular displacement.
Fourier-Transforming Means
Generally, according to the invention, the Fourier-transforming means comprises means for providing a Fourier-transformation of the scattered electromagnetic radiation giving rise to linearly displaced speckles due to an angular displacement of the object.
Or equivalently, the Fourier-transforming means comprises means for Fourier-transforming the angle of direction of the speckles generated by the scattered electromagnetic radiation into a linear coordinate of the speckles near or in the Fourier plane.
In a preferred embodiment, the linear coordinates of the Fourier-transformed speckles are the distances of speckles to the optical axis of the Fouri
Hanson Vagn Steen Grüner
Imam Gulam Husain
Rose Bjarke
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Ibsen Micro Structures A/S
Lee John R.
LandOfFree
Method and apparatus for determining angular displacement,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for determining angular displacement,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for determining angular displacement,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2444881