GB608493A - Improvements in or relating to cutting apparatus for lenses, especially spectacle-lenses - Google Patents

Abstract

608,493. Grinding lenses. BRANDT AKTIEBOLAG, J. P. May 22, 1945, No. 12747. Convention date, July 25, 1944. [Class 60] [Also in Group XX] An apparatus for cutting lenses to a desired shape and provided with a rotatable lenssupporting table and a cutting tool is characterised by the table having an aperture for the passage of rays from a projection device so that an image of a reticle is formed on a ruled disc located on the side of the lens remote from the projection device and whereby the position of the optical centre of the lens relative to its final contour may be determined and by the cutting tool being controlled by the rotation of a pattern or template having the shape of the peripheral contour to which the lens is to be cut. As shown, a frame 2 is slidable on a base 1 and carries a projection system including a collimating lens 5 whereby an image of a reticle 4 is formed on a ruled disc 11 and viewed by an ocular 12, the light from the projection device passing through an aperture in a rotatable table 14 carried by a standard 13 fixed to the base. This table is rotatable through a worm gear mechanism 20, 21 and carries by projections 16 as of rubber the lens 17 which is to be cut to the shape of a pattern 24 which is seated on the table and is rotatable therewith; a clamp 18 is spring-urged into contact with the lens and the pattern 24 is contacted by the extremity of an arm 28 which is pivoted to the frame 2 and pivotally supports at 27 a block carrying a diamond 25 with which the lens is to be cut. In use, the lens 17 and reticle 4 are adjusted until an image of the latter coincides with a hair-cross on the ruled disc 11, the lens then being optically centred in the axis by the projection system. The table 14 is then rotated and the lens is cut to the shape of the pattern 24. Decentering of the lens with respect to its new contour is effected by movement of the frame 2 before the cutting operation, the degree of the displacement being indicated by a scale and index 30, 31. When lens 17 is astigmatic, a plate 32 provided with a small aperture may be rotated about its pivot 35 to lie in the optical path and when lens 17 is bi-focal, a lens 33 may be provided in the plate. An embodiment is also described for use when a bi-focal lens is to be cut wherein two oculars are mounted on a disc rotatable on the frame 2, one of which is of a power sufficient to give a simultaneous view of the line of demarcation between the " near " and " distant " parts of the lens and a graduated disc placed in the aperture of the table. Lens 17 and pattern 24 may also be mounted on separate tables, rotatable by the same mechanism so that decentering is obtained. by the measured displacement of the pattern only. Provision is also made in this embodiment for varying the size of the cut lens while conforming to the shape of the pattern 24. Instead of a diamond, a rotating grinding-wheel or other grinding-tool may be used.