The rotating speed of the downhole motor is very important to the drilling process, so it is necessary to be measured in real-time. Here, a self-powered downhole motor rotating speed sensor, which designed as a double friction belts and a compressed friction contact structure, is proposed based on triboelectric nanogenerator. The double friction belts or any single friction belt of the sensor can be used as a self-powered rotating sensor alone, which shows a high reliability, and the compressed friction contact method increases the contact pressure of the two friction layers, thereby increasing the output signal amplitude. Test results show that the maximum output voltage and output current of the sensor with double friction belts working are respectively 15.8 V and 42.28 nA, and the maximum output power is 194.83×10-9 W when a 109 ohm resistance is connected in series, while the parameters of the sensor with single friction belt working are respectively 15.6 V and 24.17 nA, and the maximum output power is 52.22× 10-9 W when a 109 ohm resistance is connected in series. Further tests show that whether the sensor working with double belts or single belt, the measurement range is 0 to 910 r/min, the measurement error is less than 4%, and the working temperature range is 0 to 240 degrees Celsius, which shows that the sensor can meet the actual needs for the rotating speed measurement of downhole motor.

Threaded joints are key components of core drilling tools. Currently, core drilling tools generally adopt the thread structure designed by the API Spec 7-1 standard. However, fractures easily occur in this thread structure due to high stress concentrations, resulting in downhole accidents. In this paper, according to the needs of large-diameter core drilling, a core barrel joint was designed with an outer diameter of Φ135 mm and a trapezoidal thread profile. Subsequently, a three-dimensional simulation model of the joint was established. The influence of the external load, connection state and thread structure on the stress distribution in the joint was analyzed through simulations, from which the optimal thread structure was determined. Finally, a connection test was carried out on the threaded joint. The stress distribution in the joint thread was indirectly studied by analyzing gas leaks (i.e., the sealing effect) under axial tension. According to the test data and the simulation results, the final joint thread structure was optimized, which lays a good foundation for the design of a core barrel.

As a novel robot which mainly engages in the demolition and transformation of various concrete buildings, the demolition robot has developed rapidly in recent years. The impact force is mainly produced by the breaking hammer installed in the front end of the arm. As the most important part of a demolition robot, the boom arm is mainly composed of four parts including a supporting arm, a main arm, a fore arm, and a breaking hammer system. In this article, a mechanical model of the boom arm is established, and the finite element analysis obtaining the first four-order natural frequencies and modes is carried out in ANSYS Workbench. The results reveal that the resonation can be easily stimulated when a hydraulic breaking hammer is at the second-order frequency. The mounting block of the hydraulic breaking hammer, the hinge parts of the supporting arm, and the main arm are easily deformed or damaged in the Y direction by analyzing the deformation in three directions of the second-order mode. After the structure optimization, the vibration characteristics of the two parts are significantly enhanced, which provides a theoretical basis for optimizing the prototype and gives a reference in the experimental modes.