Xiuzhi Luo

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.

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.

Study of variant design of SML-based coordinate measuring machines automatic measurement plan

It is the trend of Coordinate Measuring Machine (CMM) measurement technology that creates measurement plan automatically. Based on Pro/CMM module of Pro/E software, the idea for automatic generation of the main DMIS (Dimensional Measuring Interface Standard) file of measurement plan is described. To satisfy the special measurement requirements of different customers conveniently, a method of variant design of DMIS file based on SML (Tabular Layouts of Article Characteristics) and the main DMIS file is proposed.

Module Calibration and Image Processing Based on Measurement System for 3-D Foot Shapes

A method of module calibration and image processing based on a measurement system for 3-D foot shapes is described, which contains a module calibration system for the compensation of different position errors. A double scanning process with a calibration frame structure is performed, realizing thus a mapping conversion between the two coordinate systems. With the feature points formed by the intersection of the edges of the calibration frame and the light sectioning planes, different position errors can be automatically compensated. The disadvantages caused by the gradient prediction method can be reduced. Calibration and measurement experiments were conducted with satisfactory results.

Surface measurement based on chessboard-shaped 2-D Ronchi grating method

A method for surface profile measurement using a chessboard-shaped 2-D Ronchi grating is proposed. The gradients in two orthogonal directions of the measured surface can be obtained simultaneously using a chessboard-shaped 2-D Ronchi grating, so that it is possible to reconstruct the surface profile by means of only one Ronchigram with high accuracy. The measuring principle and the design of the chessboard-shaped 2-D Ronchi grating are described. Measurements of both stationary and varying surfaces using an instrument constructed on the basis of the method were conducted with satisfactory results.

Design optimization of compound pendulum system for measurement of microthrust

A model of the compound pendulum used for measurement of micro impulses is presented. The effects of pivot friction, air friction and vibration of the stand are simulated through numerical method. To improve the measurement accuracy, it is concluded through the simulation results that the natural period of the compound pendulum should be greater than twenty times the time duration of action of the force being measured. And the moment of inertia of the compound pendulum and the pivot friction should be properly decreased to get a better sensitivity.