Key Engineering Materials Vol. 679

Abstract: A new method compensating geometric error components of a four-axis horizontal machine tool is presented in this paper. Homogeneous transformation matrices (HTMS) and error conversion are integrated in the compensation strategy. A mathematical model which contains 29 geometric error components is established based on HTMS and the errors in X, Y and Z directions are obtained through calculation. The errors in three directions are compensated by shifting the corresponding axis. But the configuration of this machine tool is X-axis, Z-axis, B-axis, C-axis without Y-axis, so the errors in X, Y and Z directions need to be converted into X, Z and C directions which is different from the traditional machine tools. The errors after conversion are used to compensation directly. This approach is significant for the error modeling and compensation which is an easy and efficient way to improve the precision of the four-axis machine tools.

Abstract: Polishing, the last manufacturing procedure in the process of optics manufacturing, has been restricted by the existed contradictory propositions of efficiency and accuracy. As a result, a variety of new combined processing techniques put forward by researchers in many countries. While, elliptical vibration polishing (short as EVP) well considers efficiency and accuracy in machining. This paper focuses on the kinematics research of EVP tools, and proves the superiority of EVP through the vibration parameter optimization. Perfect tool path gets by the impact analysis of phase difference, frequency ratio and amplitude of the polishing tool. Meanwhile the optimum frequency for EVP is studied from the cost and efficiency perspective. The simulations reveal that the perfect tool path will be obtained in the following situations: phase difference at 90°, frequency ratio at 0.909, adjusts the tool vibration amplitude in consideration of minimum curvature radius in polishing area, and appropriately select the vibration frequency.

Abstract: In this paper, an electric transmission communication system of micro-V-groove ultra-precision CNC machine with the Mitsubishi PLC is designed. Different from the traditional method using the RS232-BD board, which has to communicate with PLC by programming offline, the system we design connects PC and PLC more directly and is more suitable for micro-V-groove ultra-precision CNC machine tool because of its real time. Embed the communication system in the CNC system, all the external devices can be monitored real-timely and the machine has run successfully.

Abstract: Thermal errors cause serious dimensional errors to a workpiece in precision machining. A feed drive system generates more heat through friction at contact areas, such as the Linear encoder and the guide, thereby causing thermal expansion which affects machining accuracy. Therefore, the thermal deformation of a Linear encoder is one of the most important objects to consider for high-accuracy machine tools. This paper analyzes the increase of the temperature and the thermal deformation of a Linear encoder feed drive system. During temperature variation is measured by using thermocouples , meanwhile, the thermal error of the guide is measured by a laser interferometer. A thermal error model is proposed in this study by using back propagation neural network (BPN). An experiment is carried out to verify the thermal error of the guide under different feed rates and environmental temperature.

Abstract: Wavy fibers, fabricated via electrospinning, have been designed into many applications, such as the sensors, resonators, electromechanical systems, stretchable electronics products, flexible displays. In order to control the wavy fiber morphology, auxiliary electrodes (A-E) have been designed to control the wavy fibers deposition in near-field electrospinning (NFES), and the alternate current supplied to A-E could control fibrous amplitude and the generated frequency of the wavy fibers well. Here continue to study the wavy fiber deposited morphology via A-E in NFES in this paper, the results show that, there are still many factors would affect the fibrous amplitude, and this paper is aimed at find out the regular of the wavy fiber deposition via the A-E, which are meaningful to control wavy fiber morphology well.

Abstract: Silicon carbide, a high-strength material, has a ductile-brittle transition mechanism. In order to establish a reasonable silicon carbide abrasive belt grinding parameters to obtain high precision silicon carbide free-surface efficiently, a series of finite element simulations were conducted to comprehend the single point diamond grinding of silicon carbide using professional analysis software of nonlinear finite element in this paper. According to the differences of cutting parameter, such as cutting depth, cutting deformation of the chip and the maximum cutting force were studied. For the free-form surface with higher accuracy, the data showed that ductile machining of silicon carbide is more efficient along with the larger rake angle, the higher cutting speed and the smaller cutting depth.

Abstract: The positioning error of ultra-precision machine tools is the primary factor directly affecting the machining accuracy. It mainly depends on the machine tools guide. And its variation trend contains the same inertia as that of the machine tools movement. The variation trend of the positioning error is the derivative of a function fitted with the positioning errors of three adjacent testing points. The variation trends function is fitted with the variation trend of many points. The model of positioning error is the integral of the variation trends function. Because the variation trend of positioning error has certain inertia, the model of positioning error which is obtained in this way is more precise and more reliable than error function model which is directly fitted with limited discrete data.

Abstract: The computerize numerical control (CNC) system is one of the key factors for the development of micro v-groove machine tools to fabrication micro v-groove structures. Based on the investigation on the machining of micro v-groove structures, a developed software contains five modules: editing, automatic programming, program control, manual control and human machine interface. A3200 software based motion controller integrated with the machine characteristics is used in this study to develop the motion control functions of the micro v-groove machine tool. Meanwhile, a method is proposed to redefine the instructions of M, T and S by setting monitoring points so as to enhance the scalability of CNC system. The results show that the CNC system software is not only stable and reliable, but also satisfies the basic requirements of the ultra-precision machining of micro v-groove structures.

Abstract: For general dynamic pick and place tasks that the objects are transferred with high speed by the conveyor belt, the capability of a delta robot to track the traveling objects is very important for the efficiency. To meet the needs of precision and smooth control, a computed-torque control scheme for conveyor tracking is implemented in this paper. For higher efficiency and accuracy, computer vision system, encoder and conveyor belt region are incorporated into the control scheme. Dividing the conveyor belt into three regions, the robot is commanded to track, pick and give up according to the subregions. Conveyor belt is equipped with an encoder that provides the controller with real-time position and speed of the belt. Based upon those informations, the controller automatically compensates the end positions with respect to the belt to adjust for the position of the conveyor. Then, the conveyor tracking problem is converted to a subregional tracking problem.