Grindwheel Tilting for Ophthalmic Lens Edging Precision
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Solution Overview
Problem
The challenge lies in accurately restarting the edging of an ophthalmic lens after the initial machining operation, due to inaccuracies in centering and blocking, leading to incorrect positioning and tilting of the lens relative to the grindwheel, which results in errors in reproducing the desired radii of curvature and symmetrical machining.
Innovation Solution
A method and tool that allow the grindwheel to pivot about two distinct transverse axes, providing two degrees of freedom for tilting, enabling it to adapt to the local orientation of the lens edge face and compensate for unwanted tilting, ensuring correct machining dimensions and accurate reproduction of the desired shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the lens is centered and blocked in a first centering frame of reference, then the initial edging operation can be performed, but after unblocking and re-blocking, the lens positioning becomes inaccurate due to cumulative centering errors
Solution Approach 1:
The grindwheel maintains continuous contact with the lens edge face throughout the edging operation, eliminating the need to stop and re-center the lens. The tilting mechanism allows the grindwheel to adapt to lens orientation variations while maintaining uninterrupted machining, thus preserving the original centering accuracy throughout the entire edging process.
Solution Approach 2:
The system changes the orientation parameters of the grindwheel by allowing it to tilt about two transverse axes. This parameter change enables the grindwheel to compensate for lens positioning variations without requiring precise re-centering, thereby maintaining edging precision despite centering frame of reference changes.
2Productivity
If the lens is re-blocked after the first machining operation, then restarting edging becomes possible, but the lens tilts relative to the grindwheel causing incorrect radii of curvature
Solution Approach 1:
The grindwheel is transformed from a fixed-position component to a dynamic one that can tilt about two transverse axes. This dynamic capability allows the grindwheel to adapt to lens tilting variations during re-blocking, ensuring that the desired radii of curvature are achieved even when the lens orientation changes between operations.
Solution Approach 2:
The grindwheel performs self-adjustment by automatically tilting to match the lens edge face orientation. This self-service mechanism compensates for positioning variations without requiring external intervention or precise re-centering, enabling accurate reworking of the lens.
3Device complexity
If the grindwheel is fixed in position, then the machine structure is simple, but it cannot compensate for lens tilting and positioning errors
Solution Approach 1:
The grindwheel mounting is extended from a single-axis rotation to include tilting about two additional transverse axes. This dimensional expansion adds rotational freedom in multiple directions, enabling the grindwheel to compensate for lens positioning and orientation errors while maintaining a relatively simple mechanical structure.
Data Source
AI summary
A method of working the periphery of an ophthalmic lens (L), the periphery of the lens possessing an edge face (C) and the method including edging the edge face of the lens by machining with a first grindwheel (31) mounted to rotate about an axis of rotation (A4). According to the invention, during the edging, in addition to being free to rotate about the axis of rotation, the first grindwheel possesses two degrees of freedom to move in tilting about two distinct pivot directions that are substantially transverse to its axis of rotation.