The direct method was used to prepare polyurea lubricating grease, and the effects of several different types of additives on the extreme pressure and anti?wear performance for polyurea lubricating grease were investigated and studied. The results demonstrate that several types of additives have good compatibility with polyurea grease, and they have little undesirable influence on colloidal stability of polyurea grease, and they can also enhance thermal stability of polyurea grease. Moreover, the addition of additives can significantly improve the performance of extreme pressure and wear resistance for polyurea lubricating grease. And in the experiments, it was found that the composite multifunctional additive containing sulfur and phosphorus has a relatively better effect on improving the extreme pressure and wear resistance of polyurea lubricating grease. The research results can provide a reference basis for the improvement of extreme pressure and anti?wear property for polyurea lubricating grease, achieving a relatively optimized comprehensive performance, thereby enhancing its practical utilization performance under the harsh working conditions for high load and high speed mechanical equipment.

The paper aims to study the problem of obstacle avoidance in air?ground cooperative tracking control for the unmanned aerial helicopter (UAH),in which a new approach of designing the path obstacle avoidance plan and controller design is proposed.Initially, as for the uncertain linear UAH,by processing and judging two?dimensional environmental information within the warning range for the UAH,an obstacle avoidance strategy is proposed with the help of wall?following algorithm,and the flight angle of obstacle avoidance path and the tracking speed that can make up for bypass distance are calculated.Secondly,the proposed obstacle avoidance method is extended to the three?dimensional case,and the flight angle of the UAH is determined based on the obstacle information in the horizontal and vertical directions,which can reduce the bypass distance caused by the obstacle avoidance link as possible.Thirdly,based on two derived obstacle avoidance algorithms above,the artificial neural network (ANN) is introduced to estimate model uncertainty,and then the tracking control design schemes are established by using feedforward compensation and optimal control technologies.some simulations demonstrate the effectiveness of the proposed obstacle avoidance strategy and control algorithm.

In this work, the inner and outer loop control strategy is adopted for the unmanned aerial vehicles (UAVs) formation system. Firstly, a sliding mode control method based on memory event?triggered mechanism (METM) is proposed for the position subsystem under delay and disturbance. The second?order model is established for each UAV, and the leader?follower framework is adopted to realize the desired flight formation. Secondly, an adaptive METM is proposed to alleviate the transmission burden, in which control input feedback is introduced. For the resulting communication delay of the control input in the proposed METM and the external disturbance to the system, a sliding mode controller is designed, which maintains desirable control performance and solves the influence of communication delay and bounded disturbance to a certain extent. Thirdly, the stability of the closed?loop system is proved by applying Lyapunov theory and H_∞ control theory, and a method that facilitates solving controller gain and triggering parameter through a series of linear matrix inequalities (LMIs) is proposed. Moreover, based on the obtained virtual control quantity, a tracking controller is designed for the attitude subsystem. Finally, a simulated example is exploited to verify the effectiveness of the proposed method.

The flexible control operation technology is used to improve the oil production process of the beam pumping system, and the use of an elliptical speed drive motor is one of the solutions to realize this technology. In order to explore the law of movement of the valve ball in the pump with elliptical velocity drive and conventional circular velocity drive, the delayed opening of the valve ball under two working conditions was analyzed,and a fluid?solid coupling simulation model was established to analyze the force law of the fixed valve. The difference of the valve ball movement under the two working conditions was obtained. Finally, the correctness of the theoretical analysis was verified by the bench experiment. The results show that the rate of opening and reaching the maximum lift of the valve ball under the elliptical velocity drive is slower than that of the conventional circular velocity drive, but it seats faster, which can effectively prevent leakage and achieve the purpose of improving oil recovery efficiency.