Boxiong Wang

Highly efficient and isotope selective photo-ionization of barium atoms using diode laser and LED light.

We demonstrated a simple method to photo-ionize barium atoms using 791 nm diode laser together with 310 nm UV LED. It solved the bottle-neck problem of previous method using 791 nm diode laser and 337 nm N(2) laser, whose ionization rate was limited by the repetition rate of N(2) laser. Compared with previous method, it has advantages of high efficiency together with simple and cheap setups. By tuning the frequency of 791 nm laser to be resonant with the desired isotope, isotope selective photo-ionization has been realized.

A PLM-based automated inspection planning system for coordinate measuring machine

With rapid progress of Product Lifecycle Management (PLM) in manufacturing industry, automatic generation of inspection planning of product and the integration with other activities in product lifecycle play important roles in quality control. But the techniques for these purposes are laggard comparing with techniques of CAD/CAM. Therefore, an automatic inspection planning system for Coordinate Measuring Machine (CMM) was developed to improve the automatization of measuring based on the integration of inspection system in PLM. Feature information representation is achieved based on a PLM canter database; measuring strategy is optimized through the integration of multi-sensors; reasonable number and distribution of inspection points are calculated and designed with the guidance of statistic theory and a synthesis distribution algorithm; a collision avoidance method is proposed to generate non-collision inspection path with high efficiency. Information mapping is performed between Neutral Interchange Files (NIFs), such as STEP, DML, DMIS, XML, etc., to realize information integration with other activities in the product lifecycle like design, manufacturing and inspection execution, etc. Simulation was carried out to demonstrate the feasibility of the proposed system. As a result, the inspection process is becoming simpler and good result can be got based on the integration in PLM.

Multisensor integrated automated inspection system

It is a trend of modern measurement technology to combine the contact and non-contact measurement techniques together to realize a more efficient and high-precision inspection of manufactured products. Based on an analysis of existing optical inspection technologies and the merits and shortcomings of coordinate measuring machine (CMM) technique, we propose a multi-sensor automatic inspection system, which combines the coordinate measuring machine with non-contact optical measuring apparatus and can select automatically either of the two methods for different (simple-geometry or complex free-form) measured objects so as to raise the accuracy amd efficiency of measurement. The general planning and key components of the system are discussed.

Spatial filtering method for fringe patterns based on gray gradient

Traditional spatial filtering methods such as median filtering and mean filtering are widely used to remove additive noise in images. Images smoothed using these methods are inevitably blurred. If images are fringe patterns and filtering mask used is in fixed shape, such as a rectangle of mxn pixels, the structures of the pattern processed may be even deformed. To resolve this problem, a filtering method with varying mask based on gray gradient is proposed. This method makes full use of the feature of fringe patterns in that the gradient of gray level at a pixel is normal to the tangential direction of the fringe there. According to the method, gradient vector at a pixel is calculated first, and then the shape of the filtering mask to be used is determined based on the gradient vector. If its amplitude is smaller than a predefined value, a nxn square mask is used, on the other hand, if its amplitude is larger than the predefined value, a bar mask normal to the vector is used. Finally, the median value or mean value of the pixels in the mask is then achieved as the smoothed value of the pixel. After the same operations are applied to all pixels in the pattern sequentially, the smoothed version of the fringe pattern is achieved. A simulated fringe pattern with noise is smoothed using this method and other filtering methods for comparison, and the result shows that noise in the fringe pattern can be effectively removed and the characteristic details of the fringes can be reserved at the same time.

Image processing techniques in 3-D foot shape measurement system

The 3-D foot-shape measurement system based on laser-line-scanning principle was designed and 3-D foot-shape measurements without blind areas and the automatic extraction of foot-parameters were achieved. The paper is focused on the study of the system structure and principle and image processing techniques. The key techniques related to the image processing for 3-D foot shape measurement system include laser stripe extraction, laser stripe coordinate transformation from CCD cameras image coordinates system to laser plane coordinates system, laser stripe assembly of eight CCD cameras and eliminating of image noise and disturbance. 3-D foot shape measurement makes it possible to realize custom-made shoe-making and shows great prosperity in shoe design, foot orthopaedic treatment, shoe size standardization and establishment of a feet database for consumers.

Measurement system for 3-D foot coordinates and parameters

The 3-D foot-shape measurement system based on laser-line-scanning principle and the model of the measurement system were presented. Errors caused by nonlinearity of CCD cameras and caused by installation can be eliminated by using the global calibration method for CCD cameras, which based on nonlinear coordinate mapping function and the optimized method. A local foot coordinate system is defined with the Pternion and the Acropodion extracted from the boundaries of foot projections. The characteristic points can thus be located and foot parameters be extracted automatically by the local foot coordinate system and the related sections. Foot measurements for about 200 participants were conducted and the measurement results for male and female participants were presented. 3-D foot coordinates and parameters measurement makes it possible to realize custom-made shoe-making and shows great prosperity in shoe design, foot orthopaedic treatment, shoe size standardization, and establishment of a feet database for consumers.

Study of the effect of CCD camera noise on microscopic autofocus criteria functions

Passive focusing techniques, which are based on the analysis of image sequences to decide the optimal imaging plane position and moving direction for focusing, are widely used for stroboscopic autofocus system nowadays. When a CCD camera is used to get images, noise of camera may result in errors in the images, and cause the autofocus process inefficient. Thus it is necessary to study microscopic images affected by camera noises to choose the suitable autofocus method. Camera noises usually include photon noise, dark current noise, photo response non-uniformity noise and read-out noise. In our CCD camera-microscopic experiment system, a micro accelerometer is used as the measured object. To analyze the effect of camera noises, we add some camera noises to the images, and run the autofocus process. One of the key techniques for microscopic autofous is its criteria function. Criteria function curves of images are analyzed and compared, including image gradient energy function, variance function, Tennengrad function and Laplace function. Spatial Poisson distribution noises and spatial Gaussian distribution noises are added to images to simulate the camera noises with different expectations and variances. Experiment results show that the performances of these criteria functions are different with different noises added.

A novel synchronization method for WR system

White Rabbit precision time protocol (WR-PTP) implements sub-nanosecond synchronization of equipment in the fiber network within the range of 10km. For real applications, it needs additional auxiliary fiber link to calibration the asymmetry of the fiber link, because of the different wavelength of the uplink and downlink light. By implement only one wavelength light for both directions, we greatly simplified the calibration process and get one order time higher synchronization precision than the previous method. Without complex recalibration for each link, the new method would make the WR system much easier to be applied.

Investigating the correlation between hydrogen-maser clocks in the same place

Using fiber based frequency dissemination system, we are building Beijing regional time and frequency network. Currently, Tsinghua University (THU), the Changping site of National Institute of Metrology (NIM-Changping) and Beijing Institute of Radio Measurement (BIRM) have been linked and synchronized via the fiber network. The frequency signals of three hydrogen masers, two placed in NIM, one in BRIM are transferred to Tsinghua University, and compared with the local hydrogen maser. By this remote comparison, the absolute frequency stability of each clock as well as the correlations between the two clocks in NIM are measured and studied.

Development and application of 3-D foot-shape measurement system under different loads

The 3-D foot-shape measurement system under different loads based on laser-line-scanning principle was designed and the model of the measurement system was developed. 3-D foot-shape measurements without blind areas under different loads and the automatic extraction of foot-parameter are achieved with the system. A global calibration method for CCD cameras using a one-axis motion unit in the measurement system and the specialized calibration kits is presented. Errors caused by the nonlinearity of CCD cameras and other devices and caused by the installation of the one axis motion platform, the laser plane and the toughened glass plane can be eliminated by using the nonlinear coordinate mapping function and the Powell optimized method in calibration. Foot measurements under different loads for 170 participants were conducted and the statistic foot parameter measurement results for male and female participants under non-weight condition and changes of foot parameters under half-body-weight condition, full-body-weight condition and over-body-weight condition compared with non-weight condition are presented. 3-D foot-shape measurement under different loads makes it possible to realize custom-made shoe-making and shows great prosperity in shoe design, foot orthopaedic treatment, shoe size standardization, and establishment of a feet database for consumers and athletes.