GB816338A - Improvements in or relating to methods of generating and manufacturing a refractive surface in an optical system having a progressively variable focal power - Google Patents

Abstract

816,338. Grinding lenses &c. SOC. INDUSTRIELLE ET COMMERCIALE DES OUVRIERS LUNETIERS, COTTET, POICHET, TAGNON & CIE. March 7, 1956 [March 9, 1955], No. 7212/56. Addition to 790,310. Class 60. Relates to a process for cutting in a piece of transparent material of uniform index of refraction or in a piece of other material intended to constitute a mould, a surface of the form defined in claim 1 of the parent Specification, the surface being crossed by a principal line along which the two main radii of curvature are equal to a common value increasing progressively along the line, in which process use is made of a cutting machine adopted to cut a generating surface having a principal line, the sections of said generating surface in planes normal to the main line having at the points on the principal line radii of curvature of valves graduated according to the common values of the main radii of curvature of the progressive surface along the principal line thereof ; the process comprises the steps of rigidly disposing the machine fixedly to locate the generating surface, setting the machine into continuous cutting movement, rigidly fixing the material to be cut on a mounting, imparting to the mounting a continuous movement relative to the machine and to the generating surface, the generating surface defining the progressive surface on the material to be cut by the envelope of the successive positions of the generating surface relative to the mounting of the material to be cut and the principal line of the generating surface defining the principal line of the progressive surface by the envelope of the successive positions of the principal line of the generating surface relative to the mounting of the material to be cut, and arranging the continuous movement of the mounting relative to the generating surface so as to satisfy the condition that each element of the principal curve of the progressive surface is generated by contact at one point with the principal curve of the generating surface having the same radius of curvature as the section of the generating surface at the same point by the generating surface at the same point. The body on which the surface V is to be generated is rigidly secured on a mounting E which also carries a cam C rolling without sliding on a cam C 1 which is movable or fixed. The surface V is constantly tangential to a fixed generating surface S, the principal line G of which has the evolute g. The sections of the surface S through planes normal at points T to the line G are curves of which the centres of curvature lie on a curve W. The cams C, C 1 are so chosen that the generation, through the rolling of C on C 1 at the contact point I, and possibly through the displacement of C 1 , will give a curve V of which the centres of curvature at the points of contact with G lie constantly on W. Several applications of the principle are described.