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

1. 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 ( 31 A) 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 ( 33 A) of the contour with respect to said reference radial axis (Y′) is known;

producing an image ( 31 AI, YI) of the finished reference standard lens and of said line;

analyzing said image ( 31 AI, YI) using image-analysis means, so as to measure the actual inclination (δI) of the image ( 33 AI) of the reference part ( 33 A) 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.

2. The method as claimed in claim 1 , characterized in that the reference standard lens ( 31 A) is chosen so that its contour has at least one straight edge ( 33 A), the latter constituting the reference part of the contour.

3. The method as claimed in claim 2 , characterized in that the reference standard lens ( 31 A) is chosen so that said straight edge ( 33 A) of its theoretical finished shape is parallel to the reference radial axis (Y′), that is to say has zero theoretical inclination.

4. The method as claimed in claim 1 , characterized in that the line consists of a mark transferred onto the lens ( 7 ) to coincide with the radial axis (Y) of the grinding adapter ( 15 ).

5. The method as claimed in claim 1 , characterized in that an image of the reference standard lens ( 31 A) and of the line (Y) is produced in the following way:

a shadow of the reference standard lens ( 31 A) and of the line (Y) is projected onto a screen ( 59 ); and

this shadow is observed using a video camera ( 61 ).

6. A method of calibrating an ophthalmic lens grinding machine, of the type 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 a reference rotating radial axis (Y′) in a fixed frame of reference connected with the axis (X) of the support shaft ( 5 );

in which the angular offset (δ) between a rotating radial axis (Y) connected with a lens ( 7 ) that is to be ground and the reference rotating radial axis (Y′) is estimated using a method as claimed in claim 1 ,

and in which the control means ( 11 ) are programmed in such a way as to introduce a correction into the control laws which correction is dependent on said estimated angular offset (δ).

7. The calibration method as claimed in claim 6 , characterized in that said correction comprises increasing, in the control law, the angular position variable (θ) by the algebraic magnitude (δ) of the estimated angular offset.

8. A device for implementing a method as claimed in claim 6 , comprising:

an image-capturing device ( 61 );

image analysis means ( 63 ) connected to said image-capturing device ( 61 ), designed to measure the actual inclination (δI) of the image ( 33 AI) of a reference part ( 33 A) of the contour of an ophthalmic object ( 31 A) with respect to the image (YI) of a line featured on said ophthalmic object ( 31 A);

programming means ( 64 ) connected on the one hand to the image analysis means ( 63 ) and, on the other hand, to the control means ( 11 ) of an ophthalmic lens grinding machine ( 1 ), said programming means ( 64 ) being designed to receive an angular offset information item (δ) from the image analysis means ( 63 ) and in response to program the control means ( 11 ) of the grinding machine in such a way as to introduce a correction into the control laws as a function of said angular offset information item (δ).

9. The device as claimed in claim 8 , characterized in that it further comprises a screen ( 59 ) and means ( 55 ) of illuminating an ophthalmic object allowing the shadow of the object to be projected onto the screen ( 59 ), said screen ( 59 ) being placed in the field of view of said image-capture device ( 61 ).

10. The device as claimed in claim 9 , characterized in that it comprises a transparent support ( 53 ) for accepting the ophthalmic object, arranged between the illumination means ( 55 ) and the screen ( 59 ).

11. The device as claimed in claim 10 , characterized in that it comprises a collimator ( 57 ) arranged between the illumination means ( 55 ) and the transparent support ( 53 ) in order to make the light rays emanating from the illumination means ( 55 ) more or less mutually parallel and normal to the support ( 53 ).

12. The device as claimed in claim 9 , characterized in that the screen ( 59 ) is a frosted glass plate.

13. The device as claimed in claim 8 , characterized in that the image-capture device ( 61 ) is a video camera.

14. The method as claimed in claim 2 , characterized in that the line consists of a mark transferred onto the lens ( 7 ) to coincide with the radial axis (Y) of the grinding adapter ( 15 ).

15. The method as claimed in claim 3 , characterized in that the line consists of a mark transferred onto the lens ( 7 ) to coincide with the radial axis (Y) of the grinding adapter ( 15 ).

16. The method as claimed in claim 2 , characterized in that an image of the reference standard lens ( 31 A) and of the line (Y) is produced in the following way:

a shadow of the reference standard lens ( 31 A) and of the line (Y) is projected onto a screen ( 59 ); and

this shadow is observed using a video camera ( 61 ).

17. The method as claimed in claim 3 , characterized in that an image of the reference standard lens ( 31 A) and of the line (Y) is produced in the following way:

a shadow of the reference standard lens ( 31 A) and of the line (Y) is projected onto a screen ( 59 ); and

this shadow is observed using a video camera ( 61 ).

18. The method as claimed in claim 4 , characterized in that an image of the reference standard lens ( 31 A) and of the line (Y) is produced in the following way:

a shadow of the reference standard lens ( 31 A) and of the line (Y) is projected onto a screen ( 59 ); and

this shadow is observed using a video camera ( 61 ).

19. The method as claimed in claim 14 , characterized in that an image of the reference standard lens ( 31 A) and of the line (Y) is produced in the following way:

a shadow of the reference standard lens ( 31 A) and of the line (Y) is projected onto a screen ( 59 ); and

this shadow is observed using a video camera ( 61 ).

20. The method as claimed in claim 15 , characterized in that an image of the reference standard lens ( 31 A) and of the line (Y) is produced in the following way:

a shadow of the reference standard lens ( 31 A) and of the line (Y) is projected onto a screen ( 59 ); and

this shadow is observed using a video camera ( 61 ).