| In industrial production,it is very important to test the fatigue life of parts to ensure the safe operation of mechanical equipment.Fatigue testing machine is a common equipment to accurately test the fatigue life of materials.At present,the hydraulic cylinder is used as power source and the traditional PID algorithm is used to achieve closed-loop control in most of the conventional tension and compression fatigue testing machines on the market.In that case,the mechanical structure is complex,and the overshoot phenomenon of the control system causes the overshoot of the mechanical structure easily due to the time-varying of the parameters of the testing machine,which leads to the advanced failure of the sample,thus affecting the accuracy of the fatigue test.To solve the above problems,a set of measurement and control system of low cycle fatigue testing machine for materials is designed and developed in this paper.The system,in which fuzzy PID control algorithm to control the pulse output of servo cylinder of testing machine is used,is powered by AC servo cylinder,so as to ensure the accurate output displacement of servo cylinder.The fuzzy PID control algorithm has the advantages of strong adaptability,fast dynamic response and high control accuracy,and the servo electric cylinder has high transmission efficiency and high position accuracy up to 0.01 mm.Based on LabVIEW platform,the measurement and control system of fatigue testing machine is developed combining the advantages of both in this paper.The main work of this paper is as follows:1 The working principle of fatigue test platform is analyzed,and the hardware is selected accordingly.The hardware platform is built and the corresponding peripheral circuit is designed.2 The mathematical model of the fatigue testing machine system is established,the fuzzy PID control theory is elaborated in detail,the control strategy for the fatigue testing machine is reasoned,the fuzzy PID control module suitable for the testing platform is designed,the control strategy of the testing machine is planned in detail,the fuzzy set of the control module is determined,the fuzzy rule table is formulated,and the method of de-fuzzification is described.3 The realization method of fuzzy PID control algorithm and the development process of measurement and control program are described.The functions of measurement and control program,such as manual adjustment,static mechanical test,dynamic fatigue test,data collection and report generation,are developed.4 The accuracy and function of the fatigue testing machine are tested.The accuracy test shows that the fuzzy PID control algorithm is superior to the traditional PID in control accuracy and response speed,and the dynamic response speed is increased by about 16%.The functional test shows that the platform has good support for fatigue test and can meet the design requirements. |
