Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

Micro-structured functional surfaces have achieved widespread applications in various advanced scientific, technological, industrial, and engineered fields due to their excellent performances, which are vitally limited by their feasible fabrication. Currently, ultra-precision machining, typically including ultra-precision diamond turning, ultra-precision diamond milling, ultra-precision diamond scratching, ultra-precision grinding, and ultra-precision polishing, is developed as a very-promising solution for the micro-structured functional surface fabrication with high quality, high efficiency, high flexibility, and low cost. Therefore, this paper aims to briefly review the current state of the art in the investigation into ultra-precision machining characteristics of micro-structured functional surfaces with a focus on their typical advanced applications as the significant achievements of their ultra-precision machining fabrication, discuss the key challenges, and further provide new insights into ultra-precision machining of micro-structured functional surfaces for the future research and their further advanced applications.

Advances in ultra-precision machining of micro-structured functional surfaces and their typical applications

Vibration in ultra-precision machining (UPM) is an intrinsic physical phenomenon, which is a key factor influencing surface generation. With a focus on passive vibration, this paper reviews the latest research into vibration characteristics and the effect of vibration on surface generation in UPM. The opportunities and challenges facing researchers are also discussed and suggestions are made for future related studies. It is found that active vibration can possibly be employed to improve surface quality influenced by passive vibration in UPM.

A review of machine-tool vibration and its influence upon surface generation in ultra-precision machining

Fly cutting in ultra-precision machining (UPM), termed ultra-precision fly cutting (UPFC), is an intermittent cutting process in which a diamond tool is mounted with a spindle to intermittently cut a workpiece. The process offers the high flexibility necessary for fabricating freeform, micro/nano-structural surfaces, as well as hybrid structural surfaces with sub-micrometric form error and nanometric surface roughness, and its constant cutting velocity provides uniform high surface quality. However, in addition to its low machining efficiency, UPFC’s intermittent cutting process results in distinctive surface generation mechanisms, covering intermittent tool-workpiece relative motion, tool geometry imprinted into a machined surface, and surface material separation and deformation. General factors, such as cutting conditions, tool geometry, material factors (material property change, material swelling and recovery, and material separation mechanism), kinematic and dynamic errors, assembling errors, cutting strategies, tool path, and workpiece geometry, are individual to UPFC and universal in UPM. Accordingly, this paper focuses on the current investigation of fly cutting applied into surface generation in UPM. Conclusions are reached and the challenges and opportunities for further studies are discussed.

A review of fly cutting applied to surface generation in ultra-precision machining

Process chains for high-precision components with micro-scale features

Fast tool/slow slide servo (FTS/SSS) technology plays an important role in machining freeform surfaces for the modern optics industry. The surface accuracy is a sticking factor that demands the need for a long-standing solution to fabricate ultraprecise freeform surfaces accurately and efficiently. However, the analysis of cutting linearization errors in the cutting direction of surface generation has received little attention. Hence, a novel surface analytical model is developed to evaluate the cutting linearization error of all cutting strategies for surface generation. It also optimizes the number of cutting points to meet accuracy requirements. To validate the theoretical cutting linearization errors, a series of machining experiments on sinusoidal wave grid and micro-lens array surfaces has been conducted. The experimental results demonstrate that these surfaces have successfully achieved the surface accuracy requirement of 1 μm with the implementation of the proposed model. These further credit the capability of the surface analytical model as an effective and accurate tool in improving profile accuracies and meeting accuracy requirements.

A novel surface analytical model for cutting linearization error in fast tool/slow slide servo diamond turning

Fresnel lenses are gaining wider applications in optoelectronics and photonic devices. They have been evolved into arrays of individual elements with better performance and better capabilities. These arrays may also be realized with individual elements having polygonal shapes such as rectangular, hexagonal, etc to achieve a high fill factor. Due to the fact that the polygonal Fresnel lens arrays are not rotationally symmetrical, they are manufactured by using expensive lithography techniques or time consuming method of having multiple molds assembled together. This paper presents an automated 4-axis ultraprecision machining technique for manufacturing an array of hexagonal Fresnel lenses. In the proposed method, a diamond tool moves as a fixed point on a circle rolling inside a fixed circle which is analogous to a Guilloche machine. The proposed automated machining technique has been experimentally verified through successful manufacturing hexagonal Fresnel lens array in a single process, without having separated sections assembled as a single master mold. From the results, an excellent surface finish and good profile accuracy are also achieved. The developed automated Guilloche machining technique also paves the way for the promising challenges to remove manufacturing barriers of machining freeform surfaces with complex curvatures.

An automated Guilloche machining technique for the fabrication of polygonal Fresnel lens array

A review of recent advances in fabrication of optical Fresnel lenses

Most of commercial CAM software solutions (SolidCAM, Unigraphics and etc.) are commonly employed for generating tool paths on machining of freeform surfaces. However, these CAM software solutions are presently unable to support fast tool/slow slide servo diamond turning of freeform surface due to difference in coordinating systems. In contrast to traditional machining processes, fast tool/slow slide servo diamond turning is controlled by both linear and angular positions of the workpiece and is known as polar or cylindrical coordinate system. Hence, a special CAM post-processor is required to generate the spiral tool trajectory in fast tool/slow slide servo diamond turning. However, these special CAM software solutions are very expensive. Manufacturers have been searching for solutions to sustain their competitive advantage in mass producing products at the shortest time to market and at a most economical cost. Hence, these drive the needs for an alternative and economical option of generating accurate to...

Dennis Wee Keong Neo

Papers

A novel surface analytical model for cutting linearization error in fast tool/slow slide servo diamond turning

An automated Guilloche machining technique for the fabrication of polygonal Fresnel lens array

A review of recent advances in fabrication of optical Fresnel lenses

CAx-technologies for hybrid fast tool/slow slide servo diamond turning of freeform surface:

Ultra-precision direct diamond shaping of functional micro features