Repetitive Excitation Control for Precise Measurement of Wave Propagation in Fluid Power Systems

Wave propagation effects in fluid power systems in general and the more specialized field of transmission line modelling have gained substantial research interest in the fluid power community. While the mathematical tools applied in computer models become more and more sophisticated, the availability of highly precise experimental data is still very limited in the fluid power literature. This paper focuses on a rather simple wave propagation experiment with a hydraulic transmission line featuring a servo-valve for excitation at one end and a blocked end boundary condition at the other end. The goal is to achieve precise control of a periodic excitation pressure waveform at the servo-valve boundary by repetitive or iterative learning control techniques. High resolution (24 bit) analog to digital conversion of the measured pressure signals together with the application of periodic averaging techniques allow for a highly precise measurement of the wave propagation dynamics including a margin of error analysis of the results. In future research, the measurement data will be used for refinement of fluid material laws for transmission line models as well as for studying the influence of geometric features like sharp edged diameter changes or elbow joints.