Papers by Author: Xin Hua Yao

Abstract: The error distribution of a machined NURBS surface is complex to describe since the machined surface isnt that easy to obtain. A new method for machined NURBS surface description based on inspection database of on-machine probing is presented. The main idea is to approximate the machined surface using the inspection data and the basis functions of the nominal NURBS surface and to get the error distribution of the surface. A virtual part with a NURBS surface is presented and its error caused by the interaction of the machine-tool-workpiece is obtained using the FEA method at the inspection points. A machined NURBS surface is achieved and the error distribution of the surface is expressed. This method provides a new way in error compensation and it will improve the machining accuracy of a NURBS surface.

Abstract: Great efforts have been made to improve the accuracy of NC machine tools, within which thermal error compensation is one of the most efficient ways. A new thermal error compensation instrument which is based on thermal modal analysis for NC machine tools is introduced in this paper. OMRONsCJ2M-CPU11 is used as microcontroller, and SAILING TECHNOLOGYs STA-A08 temperature measuring modules as temperature transmitter. Through hardware and software design, high precision and stability can be achieved. By measuring several key points temperature and making use of a thermal error compensation theory, real-time thermal error compensation can be output to the machine tool, thus thermal error can be reduced.

Abstract: Thermoelectric energy harvesting is emerging as a promising alternative energy source to drive wireless sensors in mechanical, civil, and aerospace engineering systems. Typically, the waste heat from spindle units of machine tools creates obvious potential for thermoelectric generation. The structure of heat sinks on a thermoelectric generator has a great effect on the output voltage of the thermoelectric generator due to the temperature difference between hot and cold sides induced by heat transfer, so several typical structures of heat sinks are studied under different rotation speed of the spindle. According to the simulation study, the thermal resistance of heat sinks was presented. In the experiment, the output voltages of a thermoelectric generator were measured under different rotation speed with different structures of heat sinks. Experiment and simulation shows that the two pipes structure of the heat sink can help the generator to produce more power.

Abstract: Thermoelectric energy harvesting is emerging as a promising alternative energy source for drive wireless sensors in mechanical structure monitoring. Typically, the waste heat from spindle units of machine tools creates obvious potential for thermoelectric generation. However, the problem of power gap between the power level needed by wireless sensor and what thermoelectric generators (TEGs) can provide is likely to arise in the application of thermoelectric generation. Therefore, a power management system (PMS) is needed to accumulate TEG energy first and then drive the load intermittently. This study proposes a power management system to enhance the energy harvesting and usage efficiency using three capacitors. A rotating spindle platform is set up to test the PMS, and the experimental result shows that the proposed PMS worked well when the spindle speed is 3000 rpm.

Abstract: An error mapping modeling and identification technology for the circular path test of NC machine tools is proposed. First, geometric error modeling of the NC machine tool was established and the theory of the laser measurement method was introduced. Then through further analyzing the influence of the geometric errors to circular path deviations, the error items were identified, such as the displacement errors, backlashes and squareness errors. Finally measurement and compensation experiment of circular path was conducted. The experimental results show that the geometric error modeling is feasible, and the measurement method can be set up easily and rapidly, even can be used to measure smaller radius circular path under a high feed rate condition. After compensation, the accuracy of the circular path of the machine tool is improved by 50.88%.

Abstract: Rotating spindle is the main heat source of machine tool. However, it is hard for the traditional wired sensors to get access to the temperature value in rotating environment. This is one of the largest challenges that the researchers will encounter in machine thermal analysis and machine's state monitoring, and it limits the accuracy of the machine thermal analysis and state monitoring. Recently some researcher begins to adopt wireless communication technologies into the measurement in rotating environment, which would overcome the weakness of wired sensors. This paper first describes the superiors of the popular wireless technology ZigBee. And then presents the design of a wireless temperature measurement system based on ZigBee. In the Last, the system is implemented into a wireless temperature measuring experiment. The result of the experiment proved the stability of the wireless temperature measuring system, and shows the clear advantage of wireless sensors compared with wired sensor in rotating environment.

Abstract: Wireless sensors are increasingly adopted in mechanical systems to acquire and wirelessly transmit sensed information for machine condition monitoring. For wireless sensors on spindle, the reliability of the sensors system at high rotary speed is the key factor to guarantee the validity of monitoring. How to identify sensor failure accurately and timely is essential to enhance reliability of monitoring system. To address this issue, a novel method based on the BNs was presented to distinguish sensor failure from other transmission errors. The method described causal relationships of factors inducing sensor failure by graph theory and deduced sensor failure by Bayesian statistical techniques. Experiments carried on NC machining center prove the validity of this approach.

Abstract: With the development of the CNC precision machining and the ultra-precision machining, machine tools error issue has became the most active research topics and concerned by more and more experts. In this paper, a rapid simulation software platform based on multi-body system theory and Matlab software for measurement and analysis geometric errors of CNC machine tool is presented, which includes the generation of simulated measurement data, data processing, error separation and error compensation etc. To verify the feasibility of the developed software, the sequential step diagonal vector measurement method has been analyzed. The experimental results show that after error compensation the machine performance is improved by 39%. It demonstrates that the sequential step diagonal vector measurement method could significantly improve the machine accuracy and the developed software platform is reliable. This platform is not only effective for step diagonal vector measurement method, but also can be applied to other measurements. Therefore, the software platform provides a fast, reliable and objective tool for machine error measurement and analysis.

Abstract: Considering the development of cooperative design and internet-based manufacturing and in order to manage the manufacturing process more efficiently, a unit of remote intelligent fault-diagnosis based on Bayesian Networks was designed and a software based on internet was realized. The establishment of such system will enable efficient cooperation between CNC machine tools and users as well as maintainers.

Abstract: To describe the modular structure of numerical control (NC) system and deal with the problem of interference between modules in software reliability analysis, a module dependency graph (MDG) was presented and a scenario-based scheme was proposed. MDG describes reliability of module in different application environment, module dependency and structure of software with establishing maps among modules, execution scenarios and reliability. According to the information shown in MDG, an algorithm based on the idea of traversing directed graph in graph theory was proposed. The algorithm calculates the reliability of scenario with breadth-first principle. The reliability of system could be obtained from reliability and running frequency of scenario. The scheme eliminates the defects of the conventional methods which ignore module correlation. Case study proves the scheme could evaluate the reliability of NC software effectively.