Method of grooving or counter-beveling the periphery of an ophthalmic lens
A method for grooving or counter-beveling the periphery of an opthamalic lens in a grinding machine is provided. The grinding machine includes a lens support with a mechanism configured to rotate the lens about a first axis, a grooving or counter-beveling wheel rotatable about a second axis which can be tilted relative to the first axis, and a mechanism to adjust the angle of tilt of the second axis relative to the first axis. Initially, a profile for the groove is determined. A single treatment angle corresponding to the profile is calculated, and the angle of tilt of the second axis is adjusted to the value of the single treatment angle. A groove or counter-bevel is ground into the periphery of the lens with the angle of tilt remaining constant throughout the grinding.
1. A method of grooving or counter-beveling the periphery of an ophthalmic lens in a grinding machine, the machine comprising:
a lens support provided with a mechanism configured to drive the lens in rotation about a first axis;
a grooving or counter-beveling wheel mounted on a drive shaft and rotatable about a second axis;
a mechanism configured to relatively position the grooving or counter-beveling wheel along the first axis; and
a mechanism configured to adjust an angle of tilt of the second axis relative to the first axis;
the method comprising:
determining a profile for a groove or a counter-bevel;
calculating a single treatment angle corresponding to said profile;
adjusting the angle of tilt of the second axis relative to the first axis to the value of the single treatment angle; and
grinding the groove or the counter-bevel in the lens by rotating the lens about the first axis, such that a width of the groove or the counter-bevel is constant, while maintaining said angle of tilt constant and equal to the value of the single treatment angle at all rotational positions of the lens as the lens is rotated about the first axis.
2. A method according to claim 1 , wherein the single treatment angle is calculated as an increasing function of a mean base of the profile of the groove or counter-bevel.
3. A method according to claim 1 , wherein the single treatment angle is calculated as an increasing function of a mean radius of curvature of the profile of the groove or the counter-bevel.
4. A method according to claim 2 , wherein the single treatment angle is calculated as an increasing function of a mean radius of curvature of the profile of the groove or the counter-bevel.
5. A method according to claim 4 , wherein the single treatment angle is calculated as an increasing function of the mean base of the profile of the groove or counter-bevel, and wherein the single treatment angle is calculated as an increasing function of the product of said mean base multiplied by said mean radius of curvature.
6. A method according to claim 5 , wherein the single treatment angle is calculated using the formula:
α
0
=
arccos
(
1
-
f
mean
×
δ
mean
530
)
where:
α 0 is the single treatment angle;
f mean is a mean sagitta of the profile of the groove or of the counter-bevel; and
δ mean is a mean base of the profile of the groove or of the counter-bevel.
7. A method according to claim 1 , wherein said grinding of the groove or counter-bevel comprises grinding of the groove or counter-bevel about an entirety of the periphery of the lens and maintaining the angle of tilt of the second axis relative to the first axis equal to the value of the single treatment angle throughout the grinding of the groove or counter-bevel about the entirety of the periphery of the lens.
8. A method according to claim 1 , wherein said adjusting the angle of tilt of the second axis relative to the first axis involves pivoting the drive shaft about a pivot axis.
9. A method according to claim 1 , wherein said grinding of the groove or the counter-bevel comprises grinding the groove in the lens with the grooving wheel.