Yang Liangen

A measurement system for surface topography based on three-wavelength interferometry

Optical microscopic interferometry is an important measurement method for surface topography. There is usually contradiction between enlargement of measuring interval and improvement of measuring precision. In this paper, a three- wavelength interference measurement system for surface topography based on wavelength switch and phase shift scanning is proposed. A data processing method for three- wavelength interference images is proposed, which use the phase extraction and recognition algorithm based on elliptic fitting and combined size scales of phase difference. The method can effectively improve the overall precision of surface topography measurement and expand measuring interval to nearly 27 times that of single wavelength 640 nm. Experimental results have shown that the relative measurement error of surface roughness of square wave specimen with multiple grooves is only 4.1% compared to the calibrated data which is produced by China National Institute of Metrology. Therefore, the three-wavelength interferometry method can realize high precision measurement for surface topography in a certain measuring interval.

A measuring instrument for angle based on invariant optical path and autocollimation principle

A measuring instrument for angle based on invariant optical path and autocollimation principle is proposed in the paper. The measuring principle and optical structure of the instrument are analyzed. By using analyse software, many experiments comparison between the measuring instrument for angle and commercial photoelectric autocollimator ELCOMAT3000‥ The instrument has many advantages such as small structure, high-precision and cheap cost.

A two-dimensional table with long travel and micropositioning

High-precision, long travel two-dimensional tables are widely used in ultra-precision machining, multi-dimensional measuring machine, surface grinder and advanced manufacturing fields. A two-dimensional table with long travel and micro-nano positioning is presented in this paper. The table is controlled by the combination of a computer and a FPGA (Field Programmable Gate Array) device. The moving units are consisted of AC servo motors and piezoelectric ceramics (PZT), which are used to achieve macro and micro-positioning respectively. The positioning accuracy is controlled by diffracting gratings and four-quadrant photoelectric receiver (QPD). Experimental results show that the positioning error of this table is 0.2µm, and the working range is 100×100mm2.

Research on direct digital process of inductance sensor

The equivalent circuit of inductance sensor is analyzed. Amplitude-displacement and phase-displacement equations are deduced for non-ideal carrier wave and inductance parameters. Simulation computation shows the corresponding digital curves. Considering that the traditional process method is an approximate one, a new method is presented to simultaneously obtain the amplitude and phase of output signal of sensor by simultaneity A/D and ellipse fit arithmetic. According to the characteristic of the amplitude-displacement and phase-displacement curves, we obtain displacement by phase and amplitude respectively when the sensor is close to the zero point position and away from other positions on the basis of the experiment. The experiment showed that this method can improve precision of measurement, and it can also work for the whole linear range of sensors even if the magnification is very high.