Chung-Wei Cheng

A real-time NURBS surface interpolator for precision three-axis CNC machining

Abstract Due to the fact that the cutting occurs around the cutter contact (CC) point, the efficiency and quality of CNC machining can be improved significantly if the CC velocity along the surface is kept costant. Conventional approaches to machining mainly maintain a constant cutter location (CL) velocity, so that the CC velocity along the surface is often not constant and usually results in non-uniform machining and unsatisfactory quality. To overcome this difficulty, this paper presents a novel NURBS surface interpolator that is capable of real-time generation of CL motion command for ball-end milling of NURBS surfaces and maintaining a constant CC velocity along the CC path and its intervals. For performance evaluation, a three-axis servomechanism driven by three servomotors is controlled to track segments represented by NURBS surfaces. Experimental results verify the effectiveness of the proposed method.

A real-time predictor-corrector interpolator for CNC machining

This paper presents a predictor-corrector interpolator (PCI) for the CNC machining of parts with parametric curves or surfaces. In contrast to existing parametric interpolators, the proposed method uses a simple algorithm as a predictor and the current feedrate command feedback compensation scheme as the corrector. The predictor adjusts itself according to the current feedrate command feedback, it also has the capability of predicting the next reference point of the parametric curves from the current reference point. As a result, the deviations between the current and desired feedrate commands will always fall within the specified feedrate command tolerances. This study aims at developing the mathematical analysis of the PCI, where the convergence condition is derived for the corrector. In this present approach, the user can specify either constant or variable federate and also its feedrate command accuracy. Both the simulation and experiment results are presented to demonstrate the feasibility of the proposed PCI for machining the parametric curves represented in the Non-Uniform Rational B-Spline (NURBS) form.

Fabrication of large-area hydrophobic surfaces with femtosecond-laser-structured molds

Fast replication of large-area femtosecond-laser-induced surface micro/nanostructures on plastic parts by injection molding is demonstrated. An STAVAX steel mold insert is irradiated by femtosecond laser pulses with linear or circular polarization to form periodic-like nanostructures or nanostructure-covered conical microstructures. It was then used for the process of thermal injection molding. The process provides high-volume manufacturing means to generate hydrophobic enhanced plastic parts, which is expected to be widely used in consumables and chemical/biomedical device industries.

Nanostructured Ag surface fabricated by femtosecond laser for surface-enhanced Raman scattering

Femtosecond laser was employed to fabricate nanostructured Ag surface for surface-enhanced Raman scattering (SERS) application. The prepared nanostructured Ag surface was characterized by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The FESEM images demonstrate the formation of nanostructure-covered femtosecond laser-induced periodic surface structure, also termed as ripples, on the Ag surface. The AFM images indicate that the surface roughness of the produced nanostructured Ag substrate is larger than the untreated Ag substrate. The XRD and XPS of the nanostructured Ag surface fabricated by femtosecond laser show a face centered cubic phase of metallic Ag and no impurities of Ag oxide species. The application of the produced nanostructured Ag surface in SERS was investigated by using rhodamine 6G (R6G) as a reference chemical. The SERS intensity of R6G in aqueous solution at the prepared nanostructured Ag surface is 15 times greater than that of an untreated Ag substrate. The Raman intensities vary linearly with the concentrations of R6G in the range of 10(-8)-10(-4)M. The present methodology demonstrates that the nanostructured Ag surface fabricated by femtosecond laser is potential for qualification and quantification of low concentration molecules.

Feedrate control for non-uniform rational B-spline motion command generation

Abstract This paper presents a real-time feedrate-controlled interpolator (FCI) for accurate feedrate control of computer numerical controlled (CNC) machine tools along non-uniform rational B-spline (NURBS) curves for precision machining. Unlike most of the existing interpolators that are developed based on the Taylors expansion, the proposed method uses a predictor—corrector algorithm instead. In the predictor stage, an efficient algorithm is used to estimate the servo command of the next sampling time, and in the corrector stage, the errors arising from the prediction can be corrected. This study conducts an extensive mathematical analysis of the FCI, where the criterion for selecting the sampling period, i.e. sampling period bound, is also established. The experimental results are presented to demonstrate the feasibility of the proposed FCI for machining the NURBS curves.

Fabrication of pillared PLGA microvessel scaffold using femtosecond laser ablation.

One of the persistent challenges confronting tissue engineering is the lack of intrinsic microvessels for the transportation of nutrients and metabolites. An artificial microvascular system could be a feasible solution to this problem. In this study, the femtosecond laser ablation technique was implemented for the fabrication of pillared microvessel scaffolds of polylactic-co-glycolic acid (PLGA). This novel scaffold facilitates implementation of the conventional cell seeding process. The progress of cell growth can be observed in vitro by optical microscopy. The problems of becoming milky or completely opaque with the conventional PLGA scaffold after cell seeding can be resolved. In this study, PLGA microvessel scaffolds consisting of 47 μm × 80 μm pillared branches were produced. Results of cell culturing of bovine endothelial cells demonstrate that the cells adhere well and grow to surround each branch of the proposed pillared microvessel networks.

Using femtosecond laser to fabricate highly precise interior three-dimensional microstructures in polymeric flow chip.

This paper reports using femtosecond laser marker to fabricate the three-dimensional interior microstructures in one closed flow channel of plastic substrate. Strip-like slots in the dimensions of 800 μm×400 μm×65 μm were ablated with pulse Ti:sapphire laser at 800 nm (pulse duration of ∼120 fs with 1 kHz repetition rate) on acrylic slide. After ablation, defocused beams were used to finish the surface of microstructures. Having finally polished with sonication, the laser fabricated structures are highly precise with the arithmetic roughness of 1.5 and 4.5 nm. Fabricating such highly precise microstructures cannot be accomplished with nanosecond laser marking or other mechanical drilling methods. In addition, since laser ablation can directly engrave interior microstructures in one closed chip, glue smearing problems to damage molded microstructures possibly to occur during the chip sealing procedures can be avoided too.

Internal modification for cutting transparent glass using femtosecond Bessel beams

Abstract. Taking advantage of the nonlinear laser-material interaction, femtosecond lasers can process transparent materials internally on micro- or nanoscales, whose applications include fabrication of micro-optical waveguides and fluidics, as well as stealth dicing of glass, ceramics, and semiconductor materials. A femtosecond Bessel beam has a long invariant transverse intensity profile up to several millimeters with a width of a few microns. Such characteristics allow the materials processing to be completed without moving the beam focusing points as in the case of the Gaussian beam. An experimental femtosecond Bessel beam microprocessing system is built up to investigate the glass internal modification characteristics, such as the width variation and aspect ratios of modification areas. The residual stresses in the irradiated area of glass after modification are also studied using micro Raman spectrum. Finally, an application to thin glass panel cutting is demonstrated by the process of internal modification and breaking. The glass panel is well cut with the chipping on the breaking edge <1  μm.

Patterning of Crystalline ITO Using Infrared Nanosecond Fiber Laser Pulses

A method is proposed for patterning crystalline indium tin oxide (c-ITO) patterns from amorphous ITO (a-ITO) thin films on glass substrate, using infrared nanosecond fiber laser-induced crystallization followed by chemical etching. In the proposed approach, the a-ITO film is selectively transformed into a c-ITO film over a predetermined area via the laser direct writing, and the unirradiated a-ITO film is then removed using an acidic etchant solution, resulting in the formation of c-ITO pattern on the substrate because the a-ITO has a higher etching rate than the c-ITO does. The fabricated c-ITO patterns are observed using optical microscopy and scanning electron microscopy (SEM). The crystalline, optical, electrical properties were measured by X-ray diffraction (XRD), a spectrophotometer, and a two probe station, respectively. The experimental results show that a high pulse repetition rate reduces thermal shock and yields a corresponding improvement in the physical properties of the c-ITO patterns.

Accurate feedrate control of CNC machine tools along NURBS curves

This paper presents a feedrate-controlled interpolator for accurate feedrate control of CNC machine tools along NURBS curves for precision CNC machining. Unlike most existing interpolators, usually based on the Taylor expansion, the proposed method uses an Adams-Moulton predictor-corrector algorithm instead. An upper bound on the sampling interval is established, which guarantees convergence of the corrector iterations (within each interval). Experimental results are presented to demonstrate the effectiveness of the proposed interpolator for machining curved paths defined by NURBS.