Ophthalmic Lens Machining Parameter Optimization
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Solution Overview
Problem
Current methods for surfacing ophthalmic lens blanks to achieve desired optical properties are inefficient, particularly in reducing pitting and crack defects, and require longer machining times due to conventional material removal depths and advance settings.
Innovation Solution
The process involves selecting a material with a higher pitting appearance threshold at reduced material removal depths, using specific pass depth and advance settings for finishing surfaces, and optimizing roughing and finishing tool configurations to minimize total machining time, including using polythiourethane materials and tools with defined radius of curvature and pitch settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional material removal depths and advance settings are used in surfacing machining, then the machining process is simpler to implement, but the machining time is longer and pitting defects occur more frequently
Solution Approach 1:
The patent applies parameter changes by optimizing the relationship between finishing advance setpoint and material removal depth. Specifically, it establishes that the finishing advance setpoint should be between 85-99% of the pitting appearance threshold, and the finishing pass depth should be between 0.015-0.075mm. These parameter optimizations reduce machining time by at least 15% while preventing pitting defects, directly resolving the contradiction between productivity and process complexity.
2Productivity
If larger finishing advance setpoint is used to increase machining speed, then productivity improves, but pitting defects appear on the surface
Solution Approach 1:
The patent implements feedback by establishing a closed-loop control mechanism where the finishing advance setpoint is determined as a percentage (85-99%) of the pitting appearance threshold. This feedback-based approach allows the system to operate at optimal speeds while automatically preventing pitting defects, as the advance setpoint is continuously adjusted relative to the material's specific pitting threshold characteristics.
Solution Approach 2:
The patent applies preliminary anti-action by proactively setting the finishing advance setpoint below the pitting appearance threshold (at 85-99% of the threshold) before machining begins. This preventive measure ensures that pitting defects are avoided from the start, allowing the use of higher advance setpoints that improve productivity without sacrificing surface quality.
3Manufacturing precision
If finishing pass depth is increased to remove cracks more effectively, then defect removal improves, but the machining time increases significantly
Solution Approach 1:
The patent optimizes the finishing pass depth parameter to be between 0.015-0.075mm, which is much smaller than conventional values. This parameter change, combined with optimizing the finishing advance setpoint to 85-99% of the pitting threshold, allows effective crack removal while reducing machining time by at least 15%, simultaneously improving both defect removal effectiveness and productivity.
Data Source
AI summary
A method for obtaining an ophthalmic lens, includes: —the step of selecting a material that displays a threshold of pinhole formation during a machining step of a finished surface (20) in a material-removing depth (D) of 0.07 mm, which is at least 15% higher than the threshold of pinhole formation during a machining step of a finished surface in a material-removing depth (D) of 0.22 mm; —the step of selecting a set point for finishing depth of cut (A) between 0.015 mm and 0.075 mm; and—the step of selecting a set point for finishing feed between 85% and 99% of the threshold of pinhole formation for the material-removing depth (D) given by the sum of the selected set point for finishing depth of cut (A) and the blank roughness (B′).