Suping Chang

A white light interference-based atomic force probe scanning microscopy

Novel atomic force probe scanning microscopy combined with white light interference is proposed, in which the deflection of the cantilever is obtained by measuring the movement of the white light interference central fringe. The relationship between the deflection of the atomic force probe cantilever and the movement of the central fringe is analyzed, and the nonlinearity error correction method of probe cantilever deflection measurement is given. A contact operation mode which combines the displacement of the vertical scanning system and the deflection of the cantilever is presented. The self-developed AFM head can be calibrated directly by the laser interferometer of the vertical scanning system. It can be used to measure high-precision engineering surface, optical surface and micro/nanometer surface. Many experiments on the system for a gauge block surface and hard disk surface measurement are conducted, and standard gratings are used to verify the feasibility and performance of the developed method and system.

Non-uniform interpolation and re-sampling for tactile scanning measurement

In large range surface measurement by tactile scanning method, nonlinearity problems due to the change of vertical projection height of the stylus and that of the horizontal projection length of the stylus arm are unavoidable during scanning measurement, which will result in nonlinearity of the transducer in vertical direction and also non-uniform sampling interval in horizontal direction, and hence measurement and evaluation error for surface measurement. To solve this problem, current methods are mainly based on modeling and least square fitting, in which a polynomial model with many coefficients to be determined to relate sampling data to practical coordination of measurement points is given, then by least square fitting the coefficients are obtained based on a group of data from a standard sphere measurement, so that the polynomial model is obtained explicitly and sampling data can be compensated for accurate measurement. A problem in this method is the incompleteness of the model, and the standard sphere is a specific standard sphere with given diameter, which doesn’t necessarily include all possible cases with different surface curvatures. In this paper, the nonlinearity mechanism is analyzed, an explicit model based on the mechanism is built, the nonlinearity effect is investigated, and non-uniform interpolation for profile reconstruction and resampling are attempted to improve the analysis and evaluation accuracy. Finally computational and experimental testing are conducted to verify the improvement.

A controlled-force laser interference profilometer

This paper presents a controlled-force laser interference surface measuring system, which can achieve high-precision surface profile measurements in a large range. The key technology of the system is the controlled-force laser interference displacement sensor based on Michelson interference principle. The system operates in micro-force by the voice coil motor (VCM) which alters the measuring contact force in real time and reduces the scratches caused by the stylus tip on the surfaces of the tested samples. The position of the stylus can also be changed, which avoids the damage of the system when the stylus scans across high steps or deep grooves. The optical and mechanical principles of the displacement sensor, the realization method of controllable measuring force and photoelectric signal processing are discussed in this paper. Additionally, this paper introduces the two-dimensional stage used for high precision scanner, and presents primitive experimental results.

Scanning white-light interferometric measurement of free form surface based on interference fringe tracing

This paper presents the absolute measurement of free form surface based on the use of interferometric technique to obtain the absolute height of surface, which utilizes the interference fringe obtained with an interferometric microscope to locate the points of surface and obtain the height information through a three-dimensional displacement stage. A theoretical model is established for this method based on the response of interference microscope to identify the main influence factors through analysis. A measurement system is developed based on a three-dimensional stage and a Linnik interference microscope. As the key operative part, the stage has two-grade positioning accomplished by a vertical scanning displacement function mechanism with a laser interference measuring system and driven by a servo-motor and a piezo-electronic transducer respectively. Performance tests show the stage meets the requirements for the measurement of large range surface according to the zero-order interference fringe tracing measurement method. Experimental results show that the measurement system has a vertical range of 8mm, vertical resolution of 0.002μm, and a repeatability error of less than 5%.

Design and realization of controllable measuring force profilometer

In this paper the mechanical model of measuring rod of traditional stylus profilometer is established and the analysis results show that the measuring force is changed with rotation angle of the measuring rod. The impact on profile measurement of unsteady measuring force and the necessity of measuring surface of different materials with different constant measuring force are also discussed. The mechanical relations between the measuring rod and the surface are simplified by the structural change of measuring rod and a gravity center adjustment device. A voice coil motor (VCM) is added into the measuring system to control the measuring force. By adjusting the current in the coil of the VCM in real time, the measuring force can be controlled. With the controllable force, different workpieces can be measured by using different constant measuring force and the measurement results of different workpieces are given.

A Novel 3D Profilometer Based on Linear Phase Grating Interference

The nature of the surface topography significantly influences its functional performances, such as the lubrication, wear, friction, corrosion, fatigue, et al. Therefore, the need for accurate surface metrology is becoming more and more important. This paper introduces a high-precision 3D profilometer for surface metrology with the characteristic of high resolution, long measure range and low cost. The 3D profilometer consists of several parts: the micro-displacement sensor based on linear phase grating interference, the X-Y 2D platform, the column, the optoelectronic detector and its signal processing circuit, the computer and data processing software. The precise linear motion of the displacement sensor is implemented by parallel springs and its high precise displacement measurement is realized by sine phase diffraction grating. The theoretical vertical resolution of the micro-displacement sensor may achieve 0.12 nm, and the actual measuring range of the displacement sensor is 2mm, which can reach 6mm by replacing the measuring lever. The 2D platform is driven by servo motor and the double diffraction grating metrology system is adopted to measure the position of the platform. The resolution step displacement of the 2D platform is 0.2um.