Research Of Measurement And Control System For Sling Stretch Test Machine Based On Virtual Instrument

The synthetic fiber sling is widely used during shipping, rail, road and air transport, as well as during loading and unloading goods at the port and lifting & installation of engineering equipment. The main performance indicators of the sling are its maximal security load and the rate of extend. Sling must be tested by sample stretch before coming into use. The quantity of industrial polyester filament that compose the bearing core has a direct effect on the performance indicators, therefore, it leads to great mistakes for many companies to use experience for their production. Stretch test is the key point of sling's quality testing, with a direct effect on its safety and economic capability. Thus, the research of sling stretch test is very important and has become a main focus. In recent years, there is a rapid development in this field; and based on the need of further development, the research of measurement and control system for stretch test machine is proposed. The thesis analyzes the basic principles of the sling stretch test, and designs the measurement and control system based on virtual instrument.1. The structure and testing theory of the stretch test machine are analyzed. The hydraulic pressure system is used as the pressure source; and through adjusting the electromagnetic valve and electro-hydraulic proportional flow valve, the hydraulic cylinder moving direction and the sling stretching speed control has been achieved. And the control circuits of the hydraulic system have also been designed.2. The design of system hardware. The pull force and stretch length signals are transferred from the pull sensor and displacement sensor during the process of stretching. After the signal is pretreated, it is communicated to the data acquisition card. Through analysis, the control signals from the I/O interface circuits control the hydraulic cylinder action. The process data during stretching and test results will be displayed and storied in PC.3. The selection of the pull sensor and displacement sensor being based on the analyses of the theory of the pull and displacement measurement. The pull sensor is calibrated on the stretch test machine. And the mathematical model is established by least square method with the calibration data. Through experiment, the established mathematical model is proved accurate enough to meet the need of testing experiment. The hardware platform of stretch test machine of measurement and control system is consisted of PC—the center, NI USB-6009 data acquisition card and analog, digital output module etc.4. The basic structure of control software of stretch test machine is designed. It is made up of modules of parameter setting, data acquisition, data processing and control, data recording and playback. Measurement and control software, based upon Lab VIEW, can monitor and control sling stretching, display and record real-time testing data during the process of sling stretching test; it can meet all kinds of requirements of sling stretch test and has had successful applications.