Papers by Author: Zhi Min Liu

Abstract: Coal mine roadway advanced detector, including the transmitting and receiving devices, is a kind of geophysical instrument used in coal mine roadway advanced detection based on the dynamic and directional electric field excitation method. The transmitting device emits dual frequency modulated square wave current into the excavation face and the receiving device receives potential difference of coal and rock medium generated by induced polarization, of which the frequency selection circuit is to filter the interference of the harmonics of the signal and other frequency components. The paper derived expressions of emission current. Considering the actual working conditions, the paper proposed the design requirements of the frequency selection circuit and the scheme of a controller to control multiple frequency selection filter circuits. The paper completed the design of the control circuit consisting of a microcontroller and analog switch MAX313 and the band-pass filter circuit consisting of universal active filter UAF42. According to the circuit simulation and the analysis of the data with software of multisim, it proves the design of circuit meets the requirements.

Abstract: The dynamic and electric field excitation method is a new advanced detection method. In this method, the observation frequency and of emission electrode must be reasonably selected according to the actual geological conditions of coal mine roadway to obtain the apparent frequency with adequate Induced Polarization (IP) information of geological anomalies and improve the measurement accuracy of the instrument. This paper completed the simulation of apparent frequency varying with the observation frequency and Cole-Cole model parameters with MATLAB software. The results show that the key to selecting the observation frequency mainly depends on the charge and discharge time constant .Then the paper analyzed the effect of the measured apparent frequency on the measurement accuracy. According to time constant values​​ of geological conditions in coal mine roadway, considering the efficiency and electromagnetic coupling effects on the measurement, it is best to select the observation frequency within a frequency range of 0.05~0.1Hz and the frequency ratio coefficient of 13 or 15. Now apparent IP effect is obtained.

Abstract: In order to study on the advanced detection technology and the sensitivity of the Fault geological structure based on induce polarization (IP) method, and analyze the hazards of the Fault geological structure in front of the excavation face of coal mine roadway. This paper establishes a simplified physical model of the structure and converts the model into an equivalent circuit for convenient study and then constructs an IP model of the Fault geological structure. The IP model is connected with the simulation detection model of geological abnormal mass to obtain the changed curves of the apparent resistivity and the apparent frequency under the IP mode. The curves obtained show that simulation detection results agree with the electrical parameters specified by the IP model. Therefore the basic idea of the electric method detection is verified, which will provide a feasible presupposition for the development of the coal (rock) IP effect based on the advanced detection instruments with the electric method.

Abstract: The current roadheader automatic cutting technology has been relatively mature, the pose error elimination control technology has become a research hotspot. Pitch pose error of roadheader is too large will cause automatic excavating cut roof or floor, and will make the machine lose its stability. According to the movement way and the work requirements of roadheader, this paper put forward the control method of controlling shovel plate and back support to eliminate the impact of pitching pose error , and the corresponding sensors were selected based on the actual situation. According to the kinematics analysis of shovel plate and back support, the specific control method of the research was completed. The above system has been tested on EBZ200 type roadheader and testing results is good. The study of this system is a part of the pose error elimination control for roadheader, which will lay a foundation for the detection of roadheader pose and directional tunneling.

Abstract: An advanced detector based on the dual frequency IP method was designed to solve the speed unmatched problem between the detection and excavation. The detector consists of the transmission module and the receiving module. This paper designed the circuit of the transmission module with the Proteus software and completed the control program with the Keil software. Through the co-simulation of the circuit and the control program, the transmission waveforms designed were obtained and the system proved available, which laid the foundation for the development of the transmission module of the detector.

Abstract: Rescaled range (R/S) analysis has regained in popularity as a robust tool for the examination of long-term dependence. This paper modified the R/S method to determine the periodicity. We firstly apply the modified method to artificial time series for investigating the validity of the new method. Then the proposed technique is employed to research periodicity of the sunspot time series and the results indicate the robustness of the modified method.

Abstract: To enhance the mechanical property and the bioactivity of composites, nano-hydroxyapatite (n-HA) modified monomer casting nylon-6 (n-HA/N) composites were prepared by in situ polymerization. During the synthesis of n-HA/N composite, the n-HA and caprolactam were mixed, melt and placed in the field of ultrasonic radiation. The differences between composite with ultrasonic and without ultrasonic were investigated. The tensile strength and the viscosity average molecular weight of the nylon matrix were measured. The results show that the molecular weight of the nylon matrix decreased firstly and it had the lowest value when the content of nano-hydroxyapatite was 1.6 wt.%. After that the molecular weight increased and then it began to decrease when it reached the highest value. But the tensile strength of the n-HA/N composite were improved. The ultrasonic dispersion made the n-HA more evenly dispersed in the nylon and increased the mechanical properties of the n-HA/N composites significantly. The bioactivity and moisture absorption of n-HA/N composites in simulated body fluid (SBF) were examined and compared to pure nylon. What's more, Fourier transform infrared spectrometer was used to characterize the structure of the materials formed on the surface of the composite. The results showed that moisture absorption of the n-HA/N composites was lower than that of the pure nylon. After composites impregnated 16 days in SBF, a layer of carbon hydroxyapatite (CHA) with weak crystalline was formed on the surface of sample. This phenomenon showed that the n-HA/N composites have good bioactivity.