Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-06-02
1989-03-21
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356392, G01B 908
Patent
active
048146242
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the measurement of the position of an object boundary enabling, for example, the exact measurement of the size of the object.
The measurement of position of an edge of optically formed image is conventionally carried out with the aid of an optical system equipped with a co-ordinate measuring stage and cross-wire or some form of reference marker which is aligned to coincide with the edge under investigation and the position of the edge can thus be recorded.
This method has a number of disadvantages. It is slow, dependent on subjective judgment and fatigue of operator and therefore may produce inconsistent results.
With the growing requirement for automated non-contact measuring systems there is need for rapid, precise and consistent measurement of edge position on optical images under dynamic conditions. Such measurements find use, for instance, in high precision metrology applications, where it is necessary to obtain dimensional information on engineering components.
It is an object of the present invention to provide an improved method and apparatus for measuring the position of an object boundary.
According to a first aspect of the present invention there is provided a method of measuring the position of an object boundary in which the object boundary is moved relative to a detector and an indication of the position of the object boundary relative to a datum point fixed in relation to the detector is produced continuously for recording in a recording means, and the value of the indication is recorded by the recording means on detection by the detector of the object boundary, the detection signal and the indication undergoing equal delays in their transmission to the recording means.
According to a second aspect of the present invention there is provided apparatus for measuring the position of the boundary of an object including a support for the object, optical means for forming an image of at least part of the object boundary on a screen which may be virtual, a first optical fibre of relatively small diameter coupling first area of the screen to a first light intensity responsive detector, a second optical fibre of relatively large diameter coupling from a second area of the screen substantially concentric with the first area to a second light intensity responsive detector, the support and the screen being relatively movable, comparator means for comparing the signals from the first and second detectors and producing an output signal when the two detector signals have a predetermined relationship, transducer means coupled to the support producing an electrical signal representing the position of the support relative to the screen, and recording means connected to the transducer means for recording the position of the support at the instant the comparator means produces the output signal.
According to a third aspect of the present invention there is provided a method of measuring the position of an edge comprising the steps of: placing the edge on a movable support, illuminating the edge by means of a light source, forming an image of the illuminated edge on a screen, conveying the light from a particular fixed area on the screen to a light intensity responsive detector, deriving a first electrical signal representing the light intensity at the area from the detector, deriving a second electrical signal in response to light from the light source including light other than from the area, passing the first and second electrical signals through first and second channels respectively to a comparator, the comparator producing an output signal when the first and second electrical signals have a predetermined relationship, moving the movable support so that the image of the edge on the screen moves acoss the particular area, producing a third electrical signal representing the instantaneous position of the support as it moves, conveying the third electrical signal along a third channel to a recording means, and recording a representation of the position of the support in the recording
REFERENCES:
patent: 3108727 (1963-10-01), Farber
patent: 3365699 (1968-01-01), Foster
patent: 4167678 (1979-09-01), Mischo et al.
IBM Journal of Research and Development, vol. 17, No. 6, Nov. 1973, New York (US) M. Kallmeyer et al: "Rapid, Precise, Computer-Controlled Measurement of XY-coordinates", pp. 490-499, see p. 491, paragraph 1- p. 494, paragraph 1, FIGS. 1, 3, 4.
Patents Abstracts of Japan, vol. 9, No. 101 (P-353) (1824) 2 May 1985 & JP A, 59226802 (Mitsutoyo Seiskusho K.K.).
Patents Abstracts of Japan, vol. 9, No. 199 (P-380) (1922) 16 Aug. 1985 & JP. A 6063402 (Nihon Kougaku Kogyo K.K.).
Allen Stephone B.
Nelms David C.
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