Pressure sensor: due to the pressure sensor bandwidth is higher than the system’s, usually can be

regarded as approximate proportion. So the transfer function of the pressure sensor is a K

. According to the working principle of the system and the mathematical model of control system, the system dynamic chart was shown in figure 5.

Fig.5 The block diagram of electro-hydraulic proportional pressure control system

2 Control system simulation and analysis

In the actual site, the working pressure of emulsion pump is between 24 MPa and 32 MPa. When the system pressure is higher than the 32 MPa, the relief valve discharge, and when the system pressure is lower than the 24 MPa, the auxiliary pump is started up to increase the system pressure. Therefore, this rated pressure of the system is set at 27 MPa[5]. According to the system hardware, the suitable parameter were selected, and they were be plug into dynamic equation, In this paper, simulation models of MATLAB software is built for deeper theory analysis. The result is shown in figure 6.

Applied Mechanics and Materials Vols. 190-191 863

Fig.6 The pressure response curve of control system

According to the vertical axis changes of the simulation curve graph, these can be seen that the system is stable at 27 MPa. When the constant pressure signal of 27 MPa is input, the system pressure response will fluctuates up and down as the pressure goes on, but quickly stable at the 27 MPa, that proves the system is stable. Based on the system pressure wave range, the system pressure is not more than 30 MPa, it proves that the pressure of the pressure control system can not surpass the maximum pressure value; if the pressure valve is not lower than 24 MPa, that proof the pressure of the pressure control system cannot below safety limit, the system wave in the security range, the system will not appear hydraulic shock, accord with the safety requirement of the control system at working conditions on site. Observe the horizontal axis change of the curve, something can be seen, that change of the curve in time is very quick, the system can be stable in 4 seconds, and less fluctuations in frequency, the system will not have the too big burden, no apparent vibration and noise. Overall, in control of the hydraulic proportional relief valve, pressure change slowly in safety, rational scope. The system won't be hit by hydraulic shock which can be caused by the general mechanical relief valve suddenly opened or closed, that play a good protection for the system structure and implement sealing elements, make certain the misoperation never start. The system is very suitable for coal mine which characteristic is higher safety factor.  

3 Summary

Through the research with electricity fluid proportional relief valve in place of the traditional electric hydraulic machinery relief valve, and in control of the PID controller, doing good to the emulsion pump system pressure control, so that the system meet the safety requirements on site. And recommend solutions for emulsion pump pressure which is not stable and has a severe change in pressure amplitude.

References

[1] Tang Shufang. Fully mechanized working face emulsion pump system optimization allocation[J]. Mechanical And Electrical.2009,pp. 91-96. (In Chinese) [2] Xu Zhi, Yang Zhengrui, Zhu Minhua. The application of PLC in the control of electrohydraulic proportion and servo system[J]. Machine Tool and Hydraulics. 2003, pp143-148. (In Chinese) [3] R. Juarez-Ferreras.Measurement and analysis of the roof pressure on hydraulic props in longwall[J].International Journal of Coal Geology,2008,75,pp.49-62.  [4] M. Zhong,T. Fu,C. Shi et al.Critical hydraulic pressure forecasting of water inrush in coal seam floors based on a genetic algorithm-neural network[J].CIM Magazine, 2009, pp.95-101. [5] Muthukumarappan Ramurthy,Bill Lyons,Randall B. Hendrickson et al.Effects of High Pressure-Dependent Leakoff and High Process-Zone Stress in Coal-Stimulation Treatments[J]. SPE production &operations, 2009, 24(3),pp.396-406.