Method for deducing geometrical defects of an optical article turning machine

1. A method for deducing geometrical defects of an optical article turning machine ( 1 ) that machines ophthalmic lenses by using a lens machining tool ( 24 ) that operates in three directions in said turning machine ( 1 ), comprising:

a step of manufacturing three checking pieces ( 10 ); and

a step of receiving data representative of optical and/or geometrical characteristics of said checking pieces,

wherein said step of manufacturing comprises steps of

manufacturing a first checking piece according to a first predetermined theoretical geometry at a first height in said turning machine,

manufacturing a second checking piece according to a second predetermined theoretical geometry different from said first predetermined theoretical geometry, at a second height in said turning machine, and

manufacturing a third checking piece according to a third predetermined theoretical geometry different from said first predetermined theoretical geometry and from said second predetermined theoretical geometry, at a third height in said turning machine, distinct from said first height and second height,

wherein said step of receiving data comprises a step of measuring optical and/or geometrical data representative of the optical and/or geometrical characteristics of each of said first checking piece, said second checking piece, and said third checking piece, and

wherein a perpendicular defect value (dperp) of said turning machine is generated from said measured optical and/or geometrical data according to a first direction ( 16 ) and a second direction ( 17 ) amongst said three directions, a calibration defect value (dx) of said turning machine is generated from said measured optical and/or geometrical data according to said first direction ( 16 ), and a parallelism defect value (dpara) of said turning machine is generated from said measured optical and/or geometrical data according to said first direction ( 16 ).

2. The method according to claim 1 , wherein the step of measuring optical and/or geometrical data is carried out by using a lens mapper which is configured to provide optical data.

3. The method according to claim 1 , wherein said turning machine has an overall geometrical defect able to provide an overall optical power defect on optical articles machined, which is defined by the following relationship:

D=d perp×coef perp +[ dx 0+( Z−Z 0)× d para]× C ×coef dx ,

where:

“D” is said overall optical power defect,

“dperp” is said perpendicular defect value according to said first and second directions,

“coef_perp” is a power error sensitivity according to a perpendicularity defect,

“dx0” is said calibration defect value according to said first direction,

“coef_dx” is a power error sensitivity according to a calibration defect,

“Z” and “Z 0 ” are heights at which at least two optical articles are manufactured,

“dpara” is said parallelism defect value according to said first direction, and

“C” is an average curvature at a center of said optical articles.

4. The method according to claim 3 , wherein said first, second and third checking pieces each have an overall optical power defect defined by the following respective relationships:

D 1 =d perp×coef perp +dx 1× C 1×coef dx ;

D 2 =d perp×coef perp +[ dx 1+( Z 2− Z 1)× d para]× C 2×coef dx ,

where

dx 1+( Z 2− Z 1)× d para= dx 2,

and

D 3 =d perp×coef perp +[ dx 1+( Z 3− Z 1)× d para]× C 3×coef dx ,

where

dx 1+( Z 3− Z 1)× d para= dx 3.

5. The method according to claim 3 , wherein said power error sensitivities according to perpendicularity and calibration defects (coef_perp, coef_dx) are predetermined according to the following steps:

creating defects having each a predetermined value in said turning machine ( 1 ), respectively a perpendicular defect value or a calibration defect value;

manufacturing for each defect created a checking piece according to a predetermined geometry;

measuring optical and/or geometrical data representative of optical and/or geometrical characteristics of said checking piece;

deducing, from said measured optical and/or geometrical data, a corresponding power error sensitivity according to a perpendicularity defect (coef_perp) or a power error sensitivity according to a calibration defect, depending of said defect created (coef_dx); and

storing a couple corresponding to said created defect value and said power error sensitivity which is associated.

6. The method according to claim 3 , wherein said power error sensitivity according to a perpendicularity defect (coef_perp) has a predetermined value and said first checking piece has a first predetermined average curvature (C 1 ) at its center, which is equal to zero, so that said perpendicular defect value (dperp) is directly deduced from said measured optical and/or geometrical data representative of optical and/or geometrical characteristics of said first checking piece.

7. The method according to claim 6 , wherein said power error sensitivity according to a calibration defect (coef_dx) has a predetermined value and said second checking piece has a second predetermined average curvature (C 2 ) at its center, distinct from said first predetermined average curvature (C 1 ), and said first height is equal to or distinct from said second height, so that said calibration defect value (dx) at said second height is deduced from said measured optical and/or geometrical data representative of optical and/or geometrical characteristics of said second checking piece, according to said deduced perpendicular defect value (dperp).

8. The method according to claim 3 , wherein said power error sensitivities according to perpendicularity and calibration defects (coef_perp, coef_dx) have predetermined values and said first checking piece has a first predetermined average curvature (C 1 ) at its center, which is different from zero, and said second checking piece has a second average curvature (C 2 ) at its center, distinct from said first predetermined average curvature (C 1 ) and also different to zero, and said first height is equal to said second height, so that said perpendicular defect value (dperp) and said calibration defect value (dx) are deduced from said measured optical and/or geometrical data representative of optical and/or geometrical characteristics of said first checking piece and of said second checking piece.

9. The method according to claim 7 , wherein said third checking piece has a third average curvature (C 3 ) at its center, equal to said second predetermined average curvature (C 2 ) and distinct from said first predetermined average curvature (C 1 ), so that said parallelism defect value (dpara) is deduced from said measured optical and/or geometrical data representative of optical and/or geometrical characteristics of said third checking piece, according to said deduced perpendicular defect value (dperp) and said deduced calibration defect value (dx).