Development of a nano-precision ruling engine for machining of freeform micro-scale optical surfaces

Toombs, Nicholas J.

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https://hdl.handle.net/2142/124680 Copy

Description

Title

Development of a nano-precision ruling engine for machining of freeform micro-scale optical surfaces

Author(s)

Toombs, Nicholas J.

Issue Date

2024-04-25

Director of Research (if dissertation) or Advisor (if thesis)

Ferreira, Placid M

Doctoral Committee Chair(s)

Ferreira, Placid M

Committee Member(s)

• Kapoor, Shiv G
• Salapaka, Srinivasa M
• Shao, Chenhui
• Krishnan, Girish
• Mensing, Glennys A

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Ultra-precision
• Fast Tool Servo
• Flexure
• Hydrostatic Bearing
• Freeform
• Asphere
• Micro Lens Array

Abstract

Wafer level optics (WLO) represent a promising technology with the potential to revolutionize optical system design and manufacturing, offering compactness, cost-effectiveness, and scalability for a wide range of applications including biomedical imaging, telecommunications, wavefront sensing, and augmented reality. New replication methods such as UV nanoimprint lithography leverage step and repeat techniques to realize wafer-scale mass production of WLO devices. Fundamentally however, these processes rely on an optical quality, microscale master mold with low form error and exceptional surface roughness (1- 10 nm RMS). Single point diamond machining (SPDM) remains one of the most promising methods to generate microscale freeform surfaces in a variety of metals, polymers, and ceramics. Commercially available SPDMs are designed for large-aperture, millimeter-scale optics. Micro-scale optics, on the other hand, are more difficult to produce on these machines owing to limitations involving high costs, reliance on cylindrical (lathe) coordinates, radially dependent machining conditions, and susceptibility to tool-setting errors. This work presents the development of a 3-axis, contour ruling engine (CRE) that is designed specifically for the generation of micro-scale freeform surface master molds using single point diamond machining. This CRE, featuring a first-of-its-kind hydrostatic bearing fast-tool-servo, with 120 um of travel and axes stiffness exceeding 200 N/um, has been shown to produce optical-quality freeform surfaces with form errors on the order of 100 nm PV and surface roughness of 1-10 nm RMS. This research includes the development of design philosophies for high-precision hydrostatic and flexural bearings and the fabrication and assembly of precision machine tool axes. This work also encompasses the formation of testing procedures to characterize the CRE stiffness, position resolution, range of motion, and system dynamics, and the synthesis of high bandwidth position controllers for voice coil and piezo-actuated servo systems. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and scanning confocal microscopy metrology techniques are also employed to evaluate the machined micro-surfaces and access their suitability as optical-quality master molds within the WLO production process.

Graduation Semester

2024-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2024 Nicholas Toombs

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