Non-spherical EEM Tool for Aspherical Optical Surfaces
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Solution Overview
Problem
Traditional chemical-mechanical polishing (CMP) and elastic emission machining (EEM) processes are limited in their ability to precisely machine non-spherical optical surfaces, with CMP restricted to spherical shapes and EEM requiring spherical machining elements that impose circular machining marks, which are not suitable for all optical surface profiles.
Innovation Solution
An elastic emission machining system employing a non-spherical machining element, such as toroidal, ellipsoidal, or polynomial shapes, that spins adjacent to the optical surface within a slurry to remove material with chemically reactive fine particles, allowing for precise, non-circular machining marks and improved surface roughness and precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a spherical machining element is used in elastic emission machining, then the machining process is simple and material removal is effective, but the machining mark is circular which limits the ability to machine non-spherical optical surfaces
Solution Approach 1:
The patent applies asymmetry by replacing the traditional spherical machining element with non-spherical elements (toroidal, ellipsoidal, aspherical, or free-form shapes). This asymmetric geometry allows the machining element to impart non-circular machining marks on optical surfaces, enabling precise figuring of aspherical, cylindrical, and free-form optical components that cannot be achieved with spherical elements.
Solution Approach 2:
The patent extends the concept of curvature from spherical to various non-spherical forms including toroidal, ellipsoidal, aspherical, and free-form geometries. These curved non-spherical shapes provide the necessary surface profile control to machine complex optical surfaces while maintaining the elastic emission machining process's effectiveness in material removal.
2Adaptability or versatility
If chemical-mechanical polishing is used, then spherical surfaces can be polished to high precision, but non-spherical surfaces cannot be processed
Solution Approach 1:
The patent uses asymmetric non-spherical machining elements (toroidal, ellipsoidal, aspherical, free-form) to break the circular symmetry limitation of traditional CMP. These asymmetric geometries enable the process to machine non-spherical optical surfaces while maintaining sub-nanometer RMS surface roughness and precise peak-to-valley figure error control.
Solution Approach 2:
The patent changes the geometric parameters of the machining element from spherical (single radius) to non-spherical forms with varying curvatures and shapes. This parameter change allows the same elastic emission machining process to handle diverse optical surface profiles including aspherical, cylindrical, and free-form geometries with high precision.
3Productivity
If spherical machining elements are used, then the process is well-established and reliable, but machining time for complex surfaces is extended
Solution Approach 1:
By employing non-spherical machining elements with optimized geometries (toroidal, ellipsoidal, aspherical, free-form), the patent achieves more efficient material removal and faster achieving of target surface figures. The asymmetric shapes allow better control over material removal patterns, reducing the total machining time required for complex optical surfaces compared to traditional spherical elements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves sub-nanometer RMS surface roughness and deterministic material removal, enabling the machining of complex optical surfaces with non-circular profiles, reducing machining time, and enhancing the quality of the machined surface figure.
Implementation Method 1
As the spherical machining element 64 spins, particulates within the slurry 78 are drawn through the gap between surface 72 and the spinning spherical machining element 64 by the rotational action of the spinning spherical machining element 64
Implementation Method 2
A slurry temperature control unit 80 is also provided to maintain the slurry 78 at a constant temperature so that, accordingly, the removal rate of the material from the surface 72 of the workpiece 70 does not vary during the EEM process
Implementation Method 3
A circulating pump 90 causes slurry 78 to flow through source hose 88 and return hose 92, as well as through tank 76 so that the slurry 78 within tank 76 stays substantially homogeneous in terms of temperature, particle concentration within the vehicle of the slurry
Implementation Method 4
Elastic Emission Machining, or EEM, is a process for finishing (i.e., polishing and figuring) the surface of an optical element, including spherical, aspherical, cylindrical, acylindrical, free-form, etc., such as a mirror or the surface of a lens, with great precision. A typical prior art EEM system 50 can remove material from a surface 72 of a workpiece 70 at the atomic level
Data Source
AI summary
An elastic emission machining apparatus includes a machining element having a non-spherical shape that is configured to spin about an axis of rotation, a tank, and a driving system. The tank has a chamber positioned to receive the machining element and a slurry comprising a mixture of a liquid and chemically reactive fine particles. The driving system is coupled to and configured to engage the machining element to spin about the axis of rotation adjacent to a surface of the workpiece to accelerate the chemically reactive fine particles through a gap between the machining element and the surface of the workpiece.