# Review on the Influence of Complex Stratum on the Drilling Trajectory of the Drilling Robot
## 2 Detection of Complex Formation and Measurement while Drilling Technology
### Measurement while Drilling (MWD) Technology
The measuring probe uses the power supply provided by the orifice explosion-proof computer to work. After collecting the data on the drill angle, azimuth, tool face  
Figure 4: Schematic diagram of underground wired signal transmission in coal mine. angle, etc., the data are sent to the orifice through the central wireline drill pipe, which is received and displayed by the explosion-proof computer. The measuring probe in the hole will stop working when the communication line is disconnected after completing the measurement [52; 53]. The specially designed central wireline drill pipe is used as the signal transmission channel in the mine wireline measurement while the drilling system, which can receive the two-way communication of signals inside and outside the hole while supplying power for the instruments in the hole. It is widely used with a fast transmission speed and the transmission of large amounts of data. However, there are also problems, such as the complex structure of drill pipe, high production and use costs, and the large through-hole structure of the drill pipe, which limit the overall mechanical performance of its joint parts, many faults or damages, poor anti-interference ability, suitability for sliding directional drilling of screw drill tools, and not meeting the requirements of efficient composite directional drilling of directional drilling [40; 54], whereas the wireless MWD system reduces the requirements for special drill pipes. It mainly includes mud pulse telemetry, electromagnetic wave, acoustic wave, intelligent drill pipe and optical fiber five transmission modes, among which the mud pulse and electromagnetic wave technology are relatively mature [47]. Through research on key technologies such as in-hole engineering parameter measurement, mud pulse carrier signal transmission, intermittent working mode design and control, orifice signal reception and demodulation processing, the mine wireless MWD device YHD3-1500 based on mud pulse has been developed, and its overall structure is as shown in Figure 6[55]. Figure 5: Composition of YHD2-1000 (A) Mine Wired MWD System. The working process is shown in Figure 7. The specific working principle is as follows. The probe pipe is connected to the back of the screw drilling tool during the process of drilling. The measuring nipple starts to collect the in-hole engineering parameter data such as the drilling track parameters (dip angle and azimuth angle) and the directional drilling tool status parameters (tool face angle) and codes them after detecting the stop signal of the mud pump through the probe pipe. The flow channel area of the hydraulic channel of the pulse generator is adjusted by the drive nipple according to the preset coding rules when the mud pump start signal is detected. The change of flow channel area will cause a change of flow resistance, which will lead to the change of outlet pressure of the mud pump. The pressure transmitter installed at the outlet of the mud pump collects the pressure change signal and transmits it to the explosion-proof computer. The pressure change curve is converted into borehole trajectory data by the explosion-proof computer according to the preset coding rules, and they are displayed in a data table and trajectory curve, providing the basis for borehole trajectory adjustments. After the data transmission is completed, the measuring probe tube stops working, the six channels in the pulse generator return to the initial state and the mud pump pressure returns to the normal value. Consequently, the normal drilling begins [56; 57]. The drill pipe string and coal-bearing formation is taken as the signal transmission channel by the mine electromagnetic wave wireless MWD system. It has a fast data transmission speed and low requirements for the quality of drilling flushing medium and the working stability of the drilling mud pump [47].