Study On The New Measurement Method Of Pneumatic Components' Flow-Rate Characterisics

It is necessary to accurately measure the pneumatic components'flow-rate characteristics, for it is the fundamental research of pneumatic power transmission and control technique. As an alternative one of ISO6358 measuring methods, the isothermal tank discharge method defined by the ISO/DIS6358-3, has the advantages of simplicity, effectiveness and energy-saving. However, this method has to be studied more deeply in the area of measuring accuracy, applicability and identification algorithm. On the other hand, during isothermal tank discharge the dynamic regularity such as temperature, pressure and polytropic exponent should also be studied deeply.With respect to the above mentioned issues, the detailed investigation and main conclusions are summarized as follows:(1) The identification algorithm defined by ISO/DIS6358-3 has been analyzed and improved. The effect of isothermal hypothesis, acquired pressure error and pressure differential noise to the identification algorithm is analyzed. According to those error analyses, a new least-squares minimization algorithm based on first-order center difference scheme is proposed, and its optimum step for calculation is deduced. The new algorithm has improved the identification precision of isothermal tank discharge method defined by ISO/DIS6358-3. Also the genetic algorithm is proposed to settle for the phenomena of multi-peak values(2) A new measurement method and its algorithm are proposed based on the dynamic regularity of polytropic exponent, which is tested by the stop method. The measurement result of pneumatic components'flow-rate characteristics shows that this new method has higher identification accuracy than other alternative methods. This new method can measure the pneumatic components with large sonic conductance, while the volume of isothermal tank need not be decided by the sonic conductance. (3) Some pneumatic components must work properly in a certant pressure range, such as some inner pilot valves. As a result, a single isothermal tank discharge method can not measure the flow-rate characteristics of those components. A new double-tank discharge method is proposed, and this new one can not only measure inner pilot valves, but also can measure other pneumatic systems which is required to work in some pressure range.(4) The measurement results of some pneumatic components always show the bad repetition. To study this phenonena, the flow-rate equation has been studied according to the nonlinear intensity. By the computation and comparision of inner curvature indexГN and parameter curvature indexГT of different pneumatic components'flow-rate curves, it can be concluded that different parameter curvature indexГT is the most important factor which affect the measurement repetition. To those pneumatic components with large nonlinear intensity, marginal confidence interval is calculated and profile-based t figures are ploted, which is helpful to analyze the nonlinear intensity.