Method for estimating the angular offset, method for calibrating a grinding machine for opthalmic glasses and device for carrying out said calibrating method

A method for estimating, for an ophthalmic lens grinding machine (1), the angular offset (δ) between a rotating radial axis (Y) associated with a lens that is to be ground and a reference rotating radial axis (Y′), said grinding machine (1) comprising:

• a grinding wheel (3);
• a support shaft (5) that can rotate about its axis (X) and can move with respect to the grinding wheel (3), on which support shaft an ophthalmic lens (7) can be mounted via a grinding adapter (15), such that the lens rotates as one with the shaft,
• drive means (9) designed to rotationally drive the support shaft (5) about its axis (X) and to move the support shaft (5) with respect to the grinding wheel (3);
• and
• control means (11) able to control the drive means (9) according to a preprogrammed control law connecting the relative position (r) of the support shaft (5) and of the grinding wheel (3) to the angular position (θ) of the reference rotating radial axis (Y′) in a fixed frame of reference connected with the axis (X) of the support shaft (5);
• which method comprises:
• grinding a reference standard lens (31A) on which the radial axis (Y) associated with the lens has already been embodied in the form of a line, according to a control law corresponding to a theoretical finished shape of reference standard lens, of which the theoretical inclination of a reference part (33A) of the contour with respect to said reference radial axis (Y′) is known;
• producing an image (31AI, YI) of the finished reference standard lens and of said line;
• analyzing said image (31AI, YI) using image-analysis means, so as to measure the actual inclination (δI) of the image (33AI) of the reference part (33A) with respect to the image (YI) of the line;
• and
• deducing said angular offset (δ) which is equal to the discrepancy between the measured actual inclination (δI) and the theoretical inclination.