Papers by Author: Bing Li

Abstract: Based on a cutting dynamics model, a new digital machining process model that integrates workpiece quality and machining condition information is proposed, and the mapping relationship between machine tool structural dynamics and product quality information (e.g., dimension error, surface shape) is analyzed in detail. On the basis of the digital machining process model, the condition monitoring and fault diagnosis method of the machining process is investigated, and an implementation flowchart of the method is proposed with explanations of critical techniques. Finally, the proposed model is applied to the condition monitoring and fault diagnosis of the machining process of a CNC end milling machine. The damage of its spindle bearing is detected successfully, which provides the proof for the root cause identification of machining error in the digital machining process.

Abstract: In the processing of manufacturing, the rising of temperature caused by friction heat, cutting heat, ambient temperature and other factors will lead to thermal deformation of the driving components of machine tool, so that the correct position between the tool and work piece will be changed. And at the same time, machine tool will lose its intrinsic accuracy and reduce its reliability. Especially in the precision cutting processing, machining errors caused by the thermal deformation of driving system will not be ignored, almost accounting for 40%~70% of the total errors. This paper is aided by a key project called ‘High-end CNC machine tools and basic manufacturing equipment’. By using CAE software ANSYS, the temperature field of axial driving system is gain through analyzing the steady-state thermal of machine tool. The experiment is used to capture physical picture of temperature field. At last, compared with the result of the experiment, we can know better the reliability of the analysis results. The results can be useful references for different axial driving system design in numerically controlled machine tool.

Abstract: The clearances in pitch mechanism of gun, such as barrel-guide, have important influence on firing accuracy. Since the sliding pair is the typical characteristics of slide plate of gun barrel and guide’s contact, the clearance can be simplified to the cantilever beam with a small gap. Dynamics models which influence the factors on cantilever clearance are established by cantilever clearance sets. The influence of clearance and the flexibility of clearance are simulated and vilified by numerical analysis. The results of the experiments are that the response signals in time domain reflect clearance size: in the same intensity under sinusoidal excitation, with enlargement of the clearance, the peak value of gun barrel time-domain signal is smaller. The current work can be referred by the gun firing accuracy design.

Abstract: In reverse engineering, complex free-form shaped parts are usually digitized quickly and accurately using the newly arisen non-contact measuring methods. However, they produce extremely dense point data at great rate. Not all the point data are necessary for generating a surface CAD model. Moreover, owing to inefficiencies in storing and manipulating them it takes a long time to generate a surface CAD model from the measured data. Therefore, an important task is to reduce the large amount of data. After analyzing the existing methods developed by other researchers, a new data reduction method, which based on bi-directional point cloud slicing, is presented in this paper. Using the proposed method, point cloud can be reduced while considering geometric features in both two parametric directions. Finally, a face model is used to verify the effectiveness of the proposed method and experimental results are given.

Abstract: The error compensation technique is used to improve the accuracy of non-contact high-precision measuring system. To ensure the accuracy of the high-precision non-contact four-coordinate blade profile measuring system, the geometric and thermal error compensation model is proposed in this paper. The system is composed of three orthogonal coordinate axes (X, Y and Z) and a rotation axis R. The coordinate transformation matrix can be calculated by the mathematical model of rigid body which is established according to the related theoretical analysis. Three-beam interferometer and standard gauge block are adopted to verify the geometric error of the system. In the thermal deformation error compensation, wavelet neural network model is established. The thermal and geometric error compensation methods are analyzed and the experimental results are given.

Abstract: Due to the fact that near a crack singularity, gradients of the solution are large and are also subject to abrupt changes, so that the solution cannot locally be accurately approximated by a piecewise polynomial function on a quasi-uniform mesh. Lifting wavelet finite element has good ability in modal analysis for singularity problems like a cracked pipe. The first three natural frequencies of the cracked pipe were solved with lifting wavelet finite element, and the database for crack diagnosis was obtained. The first three measured natural frequencies were employed as inputs and the intersection of the three frequencies contour lines predicted the normalized crack location and size. The experimental examples denote the method is of higher identification precision.

Abstract: This paper presents the application of the wavelet finite element methods (WFEM) and neural network to crack parameters estimation and discusses the accuracy and efficiency of this method. The crack is presented by a rotational massless spring, and the natural frequencies for various crack parameters (location and depth) are obtained through WFEM. The neural network is then applied to establish the mapping relationship between the natural frequencies and the crack parameters, which uses feed-forward multiplayer neural networks trained by back-propagation, error-driven supervised training. With this trained neural network, the crack location and depth is estimated through using the measured natural frequencies as the input. The results of a cantilever beam experiment indicate that the estimating error of crack location is less than 3%, and the error of crack depth is less than 2%.

Abstract: The phase-shifting method is widely used in 3-D profile measurement with optoelectronic technology and phase unwrapping is an important link where in. The traditional methods are too complex and have low efficiency. A novel method of evaluating absolute phase is presented in this paper. The technique combined the grey code fringe with phase shifting technique and colored encoded grating pattern. The order of the projecting fringes ) , ( y x n can be obtained from only one distortional colored image. The procedure is relatively simple in experimental setup and algorithm. In addition, the speed of measurement is faster than current phase unwrapping algorithm. The experimental results have proved the validity of this method.

Abstract: The detection technique of small module gears has a very important research and application value. In this paper, a composite measuring method is presented based on combining traditional mechanical contact measurement with optical image non-contact measurement. First of all, this paper analyzes the basic principle of composite probe composed of optical fiber stylus and CCD imaging system. The tail-end of the stylus is shaped into a micro-sphere, where a small refection mirror is designed. When the laser is transmitted through the fiber, a round facula can be seen from the CCD camera. The micro-sphere is kept contact with the surface of the measured gear at the time of measuring and the error of the measured gear will be reflected by the offset of the facula center. Meanwhile, the sub-pixel extraction algorithm for the center of facula image is presented. Then the calibration principle and method of probe system is analyzed in detail. Finally, the data processing principle of the presented method is discussed for gear measurement.

Abstract: Rapid reverse technology is one of the key technologies with which the enterprises develop new product and occupy the market rapidly. How to realize the reverse measurement and CAD geometry reconstruction rapidly and accurately is always the most important focus for the researchers. Based on the laser scanning technology, the realization principle of the laser line scanning measuring system is presented and the approaches to improve the precision are also analysed in the paper. The self-adaptation adjustment of the probe position can move the light knife image to the optimal imaging area of the CCD according to the calibration result, which will ensure the measurement precision of the CCD image. With the inner velocity loop and outer position loop feedback control, the simple axis position precision of the mechanical system can be controlled within 5um. In order to pick up the points of the light knife centre rationally and exactly, the reconstruction-disperse iteration algorithm is put forward. After processed by different iteration times, the optimal points can be obtained. The reconstruction method of curve and surface based on NURBS is also given. The paper presents the application and realization of the system at last, which realizes the curve and surface measurement with high precision.