Hydraulic Force Loading System Applied On Frozen Soil Frost Heave Experiment

This paper studied an electronic-hydraulic servo force loading system, which is applied on frozen soil frost heave experiment. This system simulates the pressure acted on the subgrade by train in low temperature situation.Consulted numerous related literatures and reference materials at home and abroad, hydraulic system and control system are designed, relative components are chosen or manufactured, and then experiment study of the system is done.At first, it studied the plant model of position and force system about valve control unsymmetrical hydraulic ram. In order to study the influence of loading accuracy brought by structure rigidity of the system, the structure rigidity is taken into account when modeling the system, and the system is thought as a two-degree of freedom system. The influence of loading accuracy brought by structure rigidity is theoretically analyzed. The simulation study of the plant model is done.Secondly, the hydraulic system is designed and components are chosen. Preamplifier, power amplifier, signal adjustment circuit and other extra circuit is designed and realized. The control scheme of computer and data acquisition card is finished. The control interface and control arithmetic is written by VC++6.0. Experiment study is done based on the substantial platform. Force loading tests with crossheads of different rigidity are done, the result of which prove that the force loading accuracy will reduce if the structure rigidity is not big enough, and the correctness of theory analysis is testified. Then, the improvement of force loading accuracy by adding dual-simple lag is theoretically analyzed, and experiments with dual-simple lag are done. The experiment results show that the control accuracy can arise to±4% by adding dual-simple lag. The system is tested with a crosshead of high rigidity and the control accuracy achieve±2% , the system run stably in a continuous period long enough, and all performance have achieved.At the last part of the thesis, according to the model established in chapter two simulation of fuzzy PID arithmetic is done, and compare between simulation results of fuzzy PID arithmetic and PID arithmetic is done. The simulation results show that dynamic quality and control accuracy can improve by using fuzzy PID arithmetic.