Key Engineering Materials Vols. 407-408

Abstract: The paper puts forward a method that the internal force greatly improves the actual accuracy of parallel machine tools, and a-2DOF redundantly actuated parallel mechanism is designed. The position and speed harmonious control conditions is studied and the force control system is devised in this paper. The experiments show that this method can greatly improve the accuracy of parallel machines. Therefore, the results provide the theoretical and experimental foundation for improving the accuracy of parallel machines by internal force.

Abstract: According to the inverse solutions of 3-RPS parallel machine tools, the mapping relationship between the geometrical errors built on the 3-RPS parallel machine tools and errors of out posture has been created, then the error model of direct solutions including all the geometrical parameter errors has been built, and this model can be directly used to analyse the accuracy of parallel mechanism. On this basis, the algorithm about error compensation has been proposed. Moreover, accuracy synthesis of 3-RPS parallel machine tools was made respectively in probabilistic synthesis method and extreme synthesis method, and at last these two methods were compared.

Abstract: In order to obtain the machining requirements of the machining features, it is necessary to develop a proper fixture locating scheme to constrain correctly the degrees of freedom (DOFs) of a workpart. In this paper, a machining-requirement-based design approach to locating scheme is for the first time created. Firstly, the relationship is established between the machining dimensions and the DOFs to be constrained theoretically. Secondly, the fixture locating scheme is established to characterize practical constrained DOFs of a workpiece in terms of the locator number and positions. As a result, locating correctness is defined according to the relationship between the theoretical constrained DOFs and the practical constrained DOFs, and then the determination algorithm of locating parameters is proposed quantitatively for the first time to design the fixture locating scheme.

Abstract: Worm cam mechanism is a common indexing mechanism which is widely used in automatic machinery. Because of its high transmission precision requirements, the mechanism has high demands on the cylinder cam. The machining methods of cylinder cam are unique and the methods of special machine tool and NC machining are the two methods that general adopted in the machining of it. In this paper, the method of CNC Programming which is used for machining cylinder cam in 5-axeses high speed DMU 70eVolution Machining Center is introduced. The machining principle of cylinder cam has been studied, and the mathematical model for CNC Programming has also been worked out. The automated compensation of cutting tool’s radius is used in this field for the first time.

Abstract: Along with the rapid development of semiconductor, photonics and ultra-precision engineering, ultra-precision positioning stages are becoming more necessary than ever. In this study, one novel XY micropositioning stage is proposed, in which bi-axis circular notch flexure and cantilever hinge mechanism are optimal designed as bearing to provide smooth and guided motion. The theoretical stiffness of stage is provided and verified by FEM analysis. Finally, the micro-positioning stage is built and its resolution is experimentally validated to be less than 4nm.

Abstract: To eliminate early failures of CNC lathes, it is necessary to study the early failure distribution to establish accurate early failure distribution model of CNC lathes. During the modeling process, the same group of failure data obeys Weibull distribution, exponential distribution, super-exponential distribution and gamma distribution at the same time. To optimize the failure distribution model, this paper used “relevant index” method by comparing the distribution function curve fitting and determined that this group of failure data fitted Weibull distribution using maximum likelihood estimation method with its shape parameter k 0.8706 and scale parameter b142.6991.

Abstract: To accommodate the nonlinear and dynamic nature of thermal elastic process, Grey System Theory (GST) is adopted. By using this theory, GM (2, 1) and GM (1, 4) models are constructed. Real cutting experiment on a turning machine is conducted to establish and validate the model performance in terms of generalization ability. The comparison indicates that GM (2, 1) and GM (1, 4) perform better than other static and dynamic models such as Back Propagation Neural Network (BP) and Auto-regression Moving Average (ARMA). In addition, each of the two proposed model has their own advantages and they can be applied in practice.

Abstract: EDM is a complex time-varying system, and its online parameters have a great influence on processing stability. In order to overcome the difficulty of EDM online parameters control, this paper designed a kind of intelligent controller, based on fuzzy control and ANN technology, to implement real-time control of EDM online parameters. The simulation results show that this controller can improve machining efficiency and enhance processing stability.

Abstract: Truing and dressing are time-consuming processes in precise finishing with super-abrasive wheels because of the hard super-abrasive grains which cause extensive wear of truer. In this paper, laser-assisted truing method for super-abrasive wheels is introduced. Feasibility of the proposed method is confirmed by fundamental experiments conducted with metal-bonded diamond wheel and pulsed Nd:YAG laser. On the surface of wheel irradiated with laser beam, it is found that the abrasive grains are degraded and the machinability of surface layer is remarkably improved.

Abstract: The paper presents a new multi-dimensional loading structure based on parallel mechanism used for testing the materials and components. The mechanics of structure is introduced, kinematics and control model is analyzed, and loadings are simulated. It shows that because various actual forces can be supplied and controlled, static and dynamic performances of components can be evaluated by this structure, with which the capacity of the load-bearing can be ensured accurately. The data obtained by this structure is very important for the design of the materials and the components.