Method of determining the position of an optical lens member

A method implemented by a computer, for determining a position of an optical lens member having a surface placed on a lens blocking ring that includes a bearing zone configured to at least partially bear on a placed known surface of the optical lens member when said known surface of the optical lens member is placed on the lens blocking ring and held by a force applied on the optical lens member, the optical lens member including another surface to be machined, the method comprising:

• providing a reference system including a main axis perpendicular to a main plane defined by two axes perpendicular to each other and to the main axis, the main axis corresponding to a main direction of the force applied on the optical lens member;
• providing blocking ring data representing the bearing zone in the reference system;
• providing optical lens member surface data representing, in the reference system, the known surface of the optical lens member to be placed on the blocking ring;
• providing position parameters defining a position of a reference point of the known surface with respect to the main plane of the reference system and an orientation, about the main axis of said known surface at said reference point;
• sampling the bearing zone into a plurality of points, the points being regrouped in a set of trios;
• selecting trios of points whose projection on the main plane forms a triangle comprising the projection on the main plane of the point of application of force;
• repositioning the known surface of the optical lens by virtually rotating the known surface about the two perpendicular axes so that the plane formed by the three projected points of each of the triple of points on the known surface of the optical lens is parallel to the plan formed by the three projected points of each of the triple of points on the ring, and virtually translating the known surface along the main axis to have a virtual contact between the tilted surface and the ring at the location of said trios of points;
• repeating the repositioning for each trio of points, eliminating each trio of points for which the difference in position along the main axis between the points of the blocking ring data and the corresponding points of the known surface of the optical lens is negative, and then selecting one of the remaining trios as the final trio of points;
• blocking the optical lens member by placing the known surface of the optical lens member on a blocking ring and blocking the optical lens member to a holding lens member, a position of the known surface of the optical lens member on the blocking ring being determined using the selected final trio of points;
• and
• manufacturing the other surface to be machined after the optical lens member is blocked on the blocking ring.