Papers by Author: Y. Gao

Abstract: For nano-positioning systems with piezoelectric actuators used for dynamic grinding control, sinusoidal command signals will used and will give additional problems compared with the commonly used step signals because of the hysteresis effects, which require a good modeling approach. The proposed approach of multiple polynomial regression with first order continuity gives a relative modeling error of 2.65%. The method reduces the error by 26.3-80.2% in comparison with the methods using the single, dual, and multiple polynomial regression with zero order continuity.

Abstract: An active cooling approach for coolant during ductile material grinding is proposed and examined. The aim is to enhance surface quality and to enhance productivity. The problem associated with the cryogenic cooling approach and the one with the chilled air approach are addressed. An active cooling prototype was developed utilizing a compact heat pump design, which is easy to use, movable, and can be easily fitted into different type of machine designs with relatively low costs. The system is based on the use of forced convection of the heat generated during the machining process. Experimental and computational studies of the effects of actively cooled coolant for grinding ductile materials are carried out. The experimental results show that the use of actively cooled coolant is able to improve surface quality by up to 29.95% on average in terms of surface roughness Ra. Computational testing results show that the heat can be taken away more effectively by using the proposed approach. The results of optical and SEM examinations also confirmed that the proposed approach is advantageous.

Abstract: For micro-positioning systems using piezoelectric actuators for precision grinding process control, sinusoidal command signals will be used and will give additional problems in comparison with the commonly used step signals due to the hysteresis effects, which require a good modeling approach. In order to avoid the discontinuity problem in obtaining the values of the piezoelectric constant, a new approach of direct mapping with polynomial fit is proposed. Theoretical and experimental studies are conducted and comparative studies are made. Compared with the single polynomial approach, the proposed method of direct mapping with polynomial fit is able to reduce the modeling error to 12.5%, which is 6.5% lower, and the problems in obtaining the values of the piezoelectric constant are avoided. The proposed approach is shown advantageous. Further studies are necessary to significantly reduce the modeling error.

Abstract: This paper proposes a sub-aperture grinding tool for loose abrasive computer controlled surfacing, which is designed to perform epicyclic motion and rotate around its centre at a rapid rate, whilst the entire mechanism revolves around a secondary centre at a slower rate. In actual process, the wear of the tool could affect the material removal function, and make the process unstable, thus in fact, it is difficult to make a deterministic manufacturing. The focus of the present paper is on wearing characteristics of sub-aperture tools and the wear evenness as the main objectives. To make a further study, material removal function of the tool is firstly established through theoretically modelling, next, a correlative function with weighted factors is built, which is suitable for specifying the wearing degree of the tool. Finally, to discover the relationship between the material removal rate and the tool wearing characteristics, and to optimize the grinding process, analysis and experiments are then carried out on a K9 glass specimen by means of three kinds of tool materials, i.e., polyurethane pad, aluminum plate and pitch based on the proposed technique and model. The results indicated that the required high efficiency and precision could be achieved by choosing proper processes.

Abstract: A high speed painting automizor system with elastic support is presented. Experimental tests of the system including the key part, the rotor-bearing system, were conducted using the experimental modal method under various working conditions. The natural frequency of the system is given and the relationship between the bearing stiffness and the natural frequency and amplitude are studied. Fault of the bearing GCr15 is analyzed. The experiment has three parts including the experimental theory, experimental design, and experimental data processing. The results will lay a solid foundation for further investigation on dynamic design, maintenance, working condition monitoring and fault detection of the painting automizor system.

Abstract: Evaluation of the dynamic parameters of a modulator based grinding machine system, which is underdamped, is presented. The modulator is one of a displacement-frequency type for dynamic manipulation of the stepping motor of a tool feed system which is part of a composite grinding system for a wide bandwidth control involving both low and high frequency signals. To obtain the parameters of the underdamped system, a method of multiple uses of the transient displacement responses to step commands is proposed to reduce assessment errors. The parameters to be obtained include damping ratio, undamped natural frequency, time constant, and settling time. The evaluation results were obtained based on the minimum of a composite error index using a second order dynamic system model for reference. The parameters will be useful for further development of the composite control for the precision machining process.

Abstract: This paper describes an X-Y stage with a plane cross grating for position feedback. The stage has a current servo motor and a piezoelectric actuator to realize coarse and fine positioning throughout the 50mm x 50mm range of travel. The objective table contacts tightly on a planar wafer to enhance the motion flatness. The horizontal positioning noise is less than 20nm. The stage has a positioning accuracy of 3µm. If a high quality grating and guide is used, it should be useful for 3D surface measurement and ultra-precision machining. The operating principle and the characteristics of the plane cross grating are presented. The internal structure is explained. The comparison result for the stage with a laser interference calibration is presented. The theoretical precision and error sources of the system including grating grid, guide and grating installation error are analyzed. Experiments on factors such as system noise, guide error and motion interference are presented and the results are analyzed.

Abstract: A nanometer profilometer in which the measuring force can be controlled is proposed. The key part is the nanometer profiling core, which consists of a voice coil motor with a short and movable voice coil and an inductive transducer. According to the A/D value of the transducer signal, the measuring force can be adjusted to approximately µN level by use of a PID control algorithm. The advantages of contact type and non-contact type profilometer are possessed by the proposed instrument.

Abstract: As a special surface texture evaluation method, motif has received much attention since it was adopted as an ISO standard which is ISO12085 1996. However, like many other evaluation methods, it is based on 2 dimensional lines. The surface itself is three dimensional in nature. 3D motif evaluation should be more suitable. Until now, no 3D motif evaluation method has yet been proposed. A key issue is 3D motif combination to determine how the evaluation should be implemented. Three types of 3D MOTIF combination methods currently used are examined. Features such as algorithm complexity and application range are investigated. We conclude that the best 3D Motif combination method is not currently available. We should select a combination method based on the need for surface function analysis. Hybrid methods are also recommended.

Abstract: For linear textures, widely exist on 3D engineering surfaces, a method for characterization based on the spectrum analysis is proposed. Through an angular spectrum analysis of the power spectrum of 3D surface signals, the directional characteristic parameters of the linear texture distribution on the surface are extracted. By using the directional parameters, the engineering surface can be roughly identified. A texture detector based on the directional Gabor wavelet transformation is used to detect the texture signals. The linear texture features of different directions and scales on a complex engineering surface can be decomposed. A weighting multi-scale correlative analyzing method is presented. The correlation analysis results of the texture features of different scales are weighted according to the significance and summed to obtain the final correlation results. Through Laplacian differential operation of the correlative output, a sharper correlative peak is obtained. This method has been successfully used to extract and identify bullet marks.