Device for the optical measurement of the edge to edge dimension of an object

Claim 1

A device for measuring an edge to edge dimension of an object, said device incorporating optical means forming a magnified image of the object in an image plane, the image clearly and distinctly showing the two edges of the object, a photosensitive member constituted by a sequence of photosensitive elements arranged in the image plane and oriented in a direction perpendicular to the edges of the image, said photosensitive member supplying a series of analog electrical signals having an amplitude which is a function of the light intensity received by each of the various elements constituting said photosensitive member, said device also comprising an analog-digital converter having an input connected to said photosensitive member and an output supplying a series of digital signals and a digital processing circuit connected to the output of said analog-digital converter and performing a discrete Fourier transformation of the signal formed by the series of digital signals, the transformation leading to a distribution of Fourier components comprising a first minimum having a value N and successive minima spaced from each other by the value N, said processing circuit being able to determine the value N and deduce from the value N the sought dimension L by the relation L=X/N, in which X is a parameter defined by calibration.

Claim 2

A device for measuring an edge to edge dimension of an object, said device incorporating optical means forming a magnified image of the object in an image plane, the image clearly and distinctly showing the two edges of the object, a photosensitive member constituted by a sequence of photosensitive elements arranged in the image plane and oriented in a direction perpendicular to the edges of the image, said photosensitive member supplying a series of analog electrical signals having an amplitude which is a function of the light intensity received by each of the various elements constituting said photosensitive member, said device also comprising an analog-digital converter having an input connected to said photosensitive member and an output supplying a series of digital signals and a digital processing circuit connected to the output of said analog-digital converter and performing a discrete Fourier transformation of the signal formed by the series of digital signals, the transformation leading to a distribution of Fourier components comprising a first minimum having a value N and successive minima spaced from each other by the value N, said processing circuit being able to determine the value N and deduce from the value N the sought dimension L by the relation L=X/N, in which X is a parameter defined by calibration.