SU1435935A1 - Method of measuring geometric dimensions of reflecting objects - Google Patents

Abstract

The invention relates to a measurement technique and can be used to determine the geometrical parameters of reflective objects. The purpose of the invention is to make it possible to measure the geometric dimensions of objects moving in a direction parallel to the illuminating beam of light. The radiation from laser 1 is divided into two beams, the first of which is directed to the surface of the object 14, and the second to the surface of the object 14 parallel to the first j is changed by the difference of their optical paths in the interval determined by the value of the catch in where D ,, 6 h - & , - upper and lower sword ALIN interval boundaries, respectively; S is the coherence length of light emission; And - the maximum amount of change in the size of an object between its points, illuminated by two beams of light; h is the minimum change in the size of an object between its points illuminated by two beams of light. The interference pattern is recorded, its contrast is measured. At the moment of maximum contrast of the interference pattern, the difference in the optical paths of the beams is recorded, according to which the required object size is judged. 1 il. Q (L

Description

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with with joint venture

The invention relates to a measurement technique and can be used to determine the geometrical parameters of reflective objects by using the principles of interferometry of reduced sensitivity.

The aim of the invention is to make it possible to measure the geometric dimensions of objects moving in a direction parallel to the illuminating light beam, due to insensitivity to object displacements, achieved by selecting a reference point on the object's surface and comparing the change in surface shape over an interval equal to beams with optical azanity of the path of these beams.

The drawing shows a schematic diagram of a device for realizing a tool for determining geometric dimensions of reflecting objects.

The device contains a series-arranged semiconductor laser 1, a beam-splitting platinum 2, compensators 3 and 4 optical paths, an electromechanical actuator 5 connected to the compensator 3 and connected to the sensor 6 angle-code, shear interferometer made in the form of a telescopic lens consisting of lenses 7 and 8 and a diffraction grating 9 installed between the lenses at the junction of their focal lengths. The telescopic object is oriented with its axis symmetrically to the normal, lowered to the point of intersection of the axes of the arms of the beam splitter plate 2 with the plane of installation of the object, and its input window is facing this plane, before the diffraction grating 9 on the axis of the shear interferometer there is an aperture 10, behind the lens 8 in the plane optically coupled to the installation plane of the object, a photodetector 11 is placed, the output of which is connected to the block 12 measuring the contrast of the interference fringes, the output of which is connected to the installation input of huge capacity apparatus 13 having an information input connected to the output of the sensor 6.

The method is carried out using this device as follows.

The beam splitting plate 2 divides the radiation of the laser 1 into two parallel-parallel beams and directs them to

object 14. Compensator 3 continuously changes the optical path difference of these beams. The light beams reflected from object 14 are combined using a shear interferometer consisting of lenses 7 and 8 and a diffraction grating 9. Aperture 10 serves to increase the average size of speckle elements — the structure of light reflected from a diffusion object 14, since the phase of each speckle is random value, the input window of the photodetector 11 must be less than its average size. The thicknesses of the plates of the compensator 3 and the adjustment of the compensator 4 are selected in such a way that the conditions

D

wokc

min

2: 2H + 8 6 2h - &.

five

0

five

Where

urine ALIC

D,

S H and h

the upper and lower limits of the interval, respectively; radiation coherence length; Respectively, the maximum and minimum values of the change in the size of an object between its point-rvm, illuminated by two beams of light.

Since the difference in the optical path in the arms of the shear interferometer continuously changes, at the time of the appearance of contrast bands in the interference field from the output of the photodetector 11, a sinusoidal signal with a variable amplitude enters the input of the block 12 for measuring the contrast of the interference bands. When the amplitude of the signal reaches its maximum value, the block 12 measuring the contrast of the interference fringes imposes a control voltage on the memory 13, which captures the information from the sensor 16 angle-code. This information characterizes the delay that the compensator 3 enters into the interferometer arm by means of the drive 5 at the moment of maximum band contrast. Thus, by knowing the thickness of plate 2, compensator A, and the geometry of the optical circuit, one can measure the change in the shapes of the object's surface over an interval equal to the distance between the illuminating beams of light. The parameter sought is proportional to the magnitude of the optical path of the compensator 3, where the proportionality factor is the reciprocal of the cosine of the angle between the normal, lowered into the plane of installation of the object, and the direction of propagation of the beams illuminating the test surface,

Claims (1)

Invention Formula The method of determining the geometrical dimensions of the reflecting objects, which consists in dividing the light emission into two beams, the first of which is directed to the object surface, combines the light beam reflected from the object surface with the second beam, records the interference pattern, measures its maximum Contrast and determine the geometrical dimensions of the object, about the fact that, in order to ensure the possibility of measuring the geometrical dimensions of objects moving in the direction paraplelny to the first beam veto, the second the beam is directed to the surface of the object parallel to the first one; they change the difference of their optical paths in the interval determined by the conditions Omax 2H + 8)  +, where d MO COP MII the upper and lower limits of the interval, respectively ;: o is the coherence length of the light emitted; H is the maximum amount of change in the size of an object between its points, illuminated by two beams of light; h is the minimum change in the size of an object between its points, illuminated by two beams of light, and at the moment of the maximum contrast of the interference pattern, the difference in the optical paths of the beams is recorded, according to which the object size is determined.