Acoustic transmission system of measurement data while drilling in underground coal mine

The underground roadway drilling is the most direct and effective technical means to prevent gas and water outburst. The conventional rotary drilling technology has become the mainstream method of the roadway drilling because of its advantages of simple technology,fast hole forming speed and low equipment requirements. However,the drilling trajectory measurement while drilling cannot be carried out in the process of drilling,which leaves a hidden risk to the safety of coal mining. In view of the key problem that conventional rotary drilling is unable to measure the drilling trajectory while drilling,the research on the acoustic transmission of measurement data while drilling is carried out to overcome the inadaptability of the existing measurement data transmission mode while drilling applied to conventional rotary drilling. First of all,by establishing the mathematical model of acoustic wave transmission in the drill string,using the simulation analysis software and setting up the acoustic wave transmission characteristics test platform,the amplitude attenuation and wave shape change rules of acoustic wave propagation in different drill string structures are obtained,which provides the theoretical basis for the determination of data transmission rate. Secondly,through the establishment of the mathematical model of the output characteristics of the rare-earth giant magnetostrictive transducer and the optimization of the parameters of the excitation coil and the pre pressure system,the acoustic signal transmitting device in the borehole is developed to provide a high-power and high-precision signal source for the acoustic transmission system. Then,aiming at the problem of waveform recognition of the received signal,by extracting multi-dimensional feature vector from the identified signal,a SVM classifier is constructed,and a waveform recognition method of multi-dimensional feature vector extraction is proposed to solve the problem of intelligent recognition of acoustic signal under the complex working conditions of coal mine. Finally,the operation effect of the system under the condition of 289. 5 m transmission distance and 10 bit / s transmission rate is verified by the MWD data transmission platform built,which proves the scientificity and effectiveness of the theoretical model,design method and overall system of each module.