Xiangqian Jiang

Fast surface measurement using wavelength scanning interferometry with compensation of environmental noise

We introduce a new optical interferometry system for fast areal surface measurement of microscale and nanoscale surfaces that are immune to environmental noise. Wavelength scanning interferometry together with an acousto-optic tunable filtering technique is used to measure surfaces with large step heights. An active servo control system serves as a phase-compensating mechanism to eliminate the effects of environmental noise. The system can be used for online or in-process measurement on a shop floor. Measurement results from two step height standard samples and a structured surface of a semiconductor daughterboard are presented. In comparison with standard step height specimens, the system achieved nanometer measurement accuracy. The measurement results of the semiconductor daughterboard, under mechanical disturbance, showed that the system can withstand environmental noise.

High stability multiplexed fibre interferometer and its application on absolute displacement measurement and on-line surface metrology

We propose a self-reference multiplexed fiber interferometer (MFI) by using a tunable laser and fiber Bragg grating (FBG). The optical measurement system multiplexes two Michelson fiber interferometers with shared optical path in the main part of optical system. One fiber optic interferometer is used as a reference interferometer to monitor and control the high accuracy of the measurement system under environmental perturbations. The other is used as a measurement interferometer to obtain information from the target. An active phase tracking homodyne (APTH) technique is applied for signal processing to achieve high resolution. MFI can be utilized for high precision absolute displacement measurement with different combination of wavelengths from the tunable laser. By means of Wavelength-Division-Multiplexing (WDM) technique, MFI is also capable of realizing on-line surface measurement, in which traditional stylus scanning is replaced by spatial light-wave scanning so as to greatly improve the measurement speed and robustness.

Three-dimensional surface characterization for orthopaedic joint prostheses.

Abstract This study attempts to investigate a range of ‘better’ methods for the characterization of the three-dimensional (3D) surface topography of orthopaedic joint prostheses. In this paper, a new characterization tool for the comprehensive identification and evaluation of functional features of these surface topographies is presented. For identification, the surface topography is investigated in a space-scale space, by employing wavelet analysis. The roughness, waviness and form involved in surface topography are consequently separated and recovered respectively. The multiscalar topographical features are identified and captured. The errors caused as a consequence of three-dimensional measurement methods can be reduced. After identification, the three-dimensional surface assessment techniques previously reported by Stout and co-workers are used for the quantitative evaluation of various surface roughness features of the or topaedic joint prostheses. Moreover, the functional properties, such as bearing area, material volume and void volume which are significantly effected by large peaks, pits and scratches are studied and the location of isolated peaks, pits and scratches in the different scales is also clearly characterized. In this work, measurement of the femoral heads and acetabular cups is carried out to demonstrate the applicability of the characterization technique for the three-dimensional surface topography of orthopaedic joint prostheses.

A simple, flexible and automatic 3D calibration method for a phase calculation-based fringe projection imaging system

An important step of phase calculation-based fringe projection systems is 3D calibration, which builds up the relationship between an absolute phase map and 3D shape data. The existing 3D calibration methods are complicated and hard to implement in practical environments due to the requirement of a precise translating stage or gauge block. This paper presents a 3D calibration method which uses a white plate with discrete markers on the surface. Placing the plate at several random positions can determine the relationship of absolute phase and depth, as well as pixel position and X, Y coordinates. Experimental results and performance evaluations show that the proposed calibration method can easily build up the relationship between absolute phase map and 3D shape data in a simple, flexible and automatic way.

Template matching of freeform surfaces based on orthogonal distance fitting for precision metrology

Freeform surfaces are widely used in advanced optical and mechanical devices. In order to assess the form quality of a freeform surface, it is required to match the measurement surface with the design template. To improve the matching efficiency and accuracy, the whole procedure is divided into two stages: rough matching and final fitting. A new rough matching method, called the structured region signature, is proposed. The structured region signature is a generalized global feature which represents the surface shape by a one-dimensional function. The template location occupying the best matching signature is considered to be the correct rough position of the measurement surface. After that the motion parameters are updated iteratively based on the orthogonal distance fitting. The dependence between the foot-point parameters of the projection points and the motion parameters is derived from the closest-distance relationship between correspondence point pairs. Numerical experiments are given to demonstrate the validity of this approach.

Investigation of relative micromotion at the stem-cement interface in total hip replacement

Abstract Cemented total hip replacement has become a standard surgical technique to treat patients with osteoarthritis and osteonecrosis. The stem—cement interface experiences fretting wear in vivo due to low-amplitude oscillatory micromotion under physiological loading, and this wear is currently becoming important as a potential mechanism for the overall wear of cemented total hip replacements. However, the relative micromotion at the stem—cement interface has not been widely reported. In the present study, a new micromotion sensor is developed that is based on the deformation of a strain gauge, and this sensor is used to probe the migration of a polished Exeter stem within a Simplex P cement mantle through an in vitro wear simulation. It is demonstrated that the stem migration value generally increases with an increase in the number of loading cycles, with a gradual decrease of migration rate. Additionally, fretting wear is successfully replicated on the stem surface, and the micropores in the cement surface are considered to contribute to initiation and propagation of the fretting damage on the stem. This is confirmed by the observation that no evidence of fretting wear is detected on the stem where the surface is in contact with the pore-free areas on the cement. This study allows a deep insight into the micromotion at the stem—cement interface, and provides evidence highlighting the significance of the micropores in the cement surface in the generation of fretting wear on a polished femoral stem.

Three dimensional measurement of the surface topography of ceramic and metallic orthopaedic joint prostheses.

The comprehensive study of surface topography of the orthopaedic joint prostheses has become very important for analysis of the wear mechanism and the performance life of the joint replacement systems. The aim of the study to investigate “best” methods for the three-dimensional (3D) surface metrology of orthopaedic joint prostheses. Characterization techniques for the iDentification and evaluation of the functional features of the bearing surface topographies has been provided in previous work [1]. This paper concentrates on addressing issues of measurement and application techniques for assessment of the 3D surface topography of the joint replacement systems by using contacting stylus instruments, atomic force microscopes (AFM), and non-contacting measurement supported by focus detection instruments and phase-shifting interferometers. The techniques are discussed according to different analysis requirements of the orthopaedic joint prostheses. This work also discusses the performances of the instruments in terms of the measurement of femoral heads. Finally, recommendations for acceptable measurement techniques and application for analyzing surface topography of orthopaedic joint prostheses are summarized. ©2000 Kluwer Academic Publishers

Surface and thickness measurement of a transparent film using wavelength scanning interferometry

A wavelength scanning interferometer for measuring the surface and thickness of a transparent film has been studied. A halogen light source combined with an acousto-optic tuneable filter is used to generate a sequence of filtered light in a Linnik interferometer, which leads to a sequence of interferograms captured by a CCD camera. When a transparent thin film is measured, the reflection signals from both the top and bottom surfaces of the film will interfere with the reference signal. At the same time, the multiple reflection signals between the two film surfaces will also interfere with each other. Effective separation of the interference signals from each other is the key to achieving a successful measurement. By performing a frequency-domain analysis, these interference signals can be separated. An optimized Fourier transform method is used in the analysis. Measurements of the top and bottom surface finishes of the film, as well as the film thickness map, have been achieved. The film needs to be more than 3 µm in optical path length, and must transparent with no absorption of light. The films refractive index needs to be known as a function of wavelength. In this paper, the theoretical analysis and simulation study of wavelength scanning interferometry for transparent film measurement is discussed. Experiments on thin film layers of Parylene N coated on a glass slide surface are studied and analyzed. Comparison study results with other contact and non-contact methods are also presented.

Iterative optimization calibration method for stereo deflectometry

An accurate system calibration method is presented in this paper to calibrate stereo deflectometry. A corresponding iterative optimization algorithm is also proposed to improve the system calibration accuracy. This merges CCD parameters and geometrical relation between CCDs and the LCD into one cost function. In this calibration technique, an optical flat acts as a reference mirror and simultaneously reflect sinusoidal fringe patterns into the two CCDs. The normal vector of the reference mirror is used as an intermediate variable to implement this iterative optimization algorithm until the root mean square of the reprojection errors converge to a minimum. The experiment demonstrates that this method can optimize all the calibration parameters and can effectively reduce reprojection error, which correspondingly improves the final reconstruction accuracy.

Invariant-Feature-Pattern-Based Form Characterization for the Measurement of Ultraprecision Freeform Surfaces

Ultraprecision freeform surfaces (UPFSs) are increasingly being used in advanced optical systems due to their superior optical properties. However, current research on the measurement of machined UPFSs is still hindered by lack of efficient and robust form characterization techniques which can characterize the form error of measured freeform surfaces with submicrometer accuracy. This paper presents an invariant-feature-pattern-based form characterization (IFPFC) method. IFPFC makes use of intrinsic surface features (e.g., Gaussian curvature) to map the surface into an orientation-independent feature pattern to represent the surface geometry. Surface matching and comparison are then undertaken in terms of feature pattern registration. Compared with conventional methods, the IFPFC is not only robust to the initial position of the measured surface relative to the design template but also computationally efficient since it does not involve much iteration. A series of computer simulations and actual measurement are conducted to demonstrate the performance and the validity of the IFPFC method in the measurement and characterization of UPFSs with submicrometer form accuracy.