METHOD AND DEVICE FOR DETERMINING THE THICKNESS OF A GLASS TUBE.

摘要

A device for determining the thickness of a glass tube provides for projecting two parallel light beams onto the wall of the tube (18) to be inspected at an angle to the normal drawn from the source of the light to the axis of the tube (18), interferometrical comparison of said light beams reflected by the walls of the tube (18), changing the optical path of one of the light beams and measuring said change of the optical path from the initial value and up to the moment of obtaining the interference picture of the maximum contrast. The distance between the optical axes of the light beams and the difference between their optical paths are changed according to the following formula (I): DELTA D = (Kt + C) Sin<2> alpha /2(n<2>-Sin<2> alpha ), DELTA L = Kt + C, where DELTA D represents the distance between the optical axes of the light beams; DELTA L represents the difference between their optical paths, in m; K represents the velocity, c; n represents refractive index of the wall of the tube; alpha represents the angle between the normal to the axis of the tube and the optical axes of the light beams, rad; C represents a constant, determined by a condition: delta < DELTA Lmin < 2 2ROOT n<2>-Sin<2> alpha . dmin - delta , DELTA Lmax > 2 2ROOT n<2>-Sin<2> alpha . dmax + delta , where: delta represents the length of the coherent radiation, m; DELTA Lmin, DELTA Lmax represents minimum and maximum values of the difference between the optical paths, m; dmin, dmax represent minimum and maximum values of the thicknesses of the tube, m. The device for implementing the method comprises an illuminating system (1), a two-beam interferometer (2) with two reflectors (6) and (11) one (6) of which is located on a modulator (8), and an axle for receiving the tube. The optical axis of the illuminating system (1) is oriented at an angle THETA to the normal to the face (17) of a cube (5), whereas the axle (13) lies in a plane oriented symmetrically to the beam plane of incidence of the system (1) in relation to the light dividing edge (12), whereas the normal drawn to the axle (13) in the plane of its location is oriented at an angle alpha , the angles THETA and alpha being interrelated according to a formula I: tg THETA = Sin<2> alpha /2(n<2>-Sin<2> alpha ) where n represents refractive index of the wall of the tube.