Research on Dynamic Characteristics of the High-Speed Cable Force Transmission

During the landing and detection missions of the Moon, Mars, and asteroids, due to the complexity and unpredictability of the landing process, it is necessary and critical to carry out simulation tests on the ground to simulate the stress state during the separation of the heat-shield from the lander. The heat-shield is a layer of shell to protect the safety of the detector during landing. The simulation test is realized by the cable-driven manipulator. The separation process is mainly divided into two stages. The first stage is the explosion of pyrotechnic products, the heat-shield is separated at high speed by the explosion of pyrotechnic products. This process is about 40 ms. The second stage is the cable traction acceleration, the heat-shield continues to accelerate and detach by pulling the rope. This process is about 0.3 s. The maximum speed is about 5 m/s.

In this paper, an attempt is made to study the dynamic model of the force transmission characteristics of the cable during the separation process. Different from the conventional dynamic model, we have two different separation stages. The huge difference in acceleration between these two stages leads to the severe vibration of the cable. Several challenging problems, such as accurate calculation of the axial force in a moving cable and stable transmission of cable force are resolved by using the current method. Firstly, the dynamics models of the two separation processes are respectively constructed by the Hamilton principle. The governing equation of the axial force of the rope is a second-order partial differential equation (PDE). In this paper, the classical assumed mode method (AMM) which is employed to discretize the governing PDE is implemented. The corresponding boundary motion conditions and trial function are introduced to solve the governing PDE. The second-order partial differential equation is solved using the spatial discrete method to obtain the force relationship of the cable during the separation. An evaluation index is proposed to illustrated the effect of the cable force transmission. The lag time represents the time when the axial force is transmitted in the cable. The stability of cable force transmission represents the deviation of the actual value of the cable force from the theoretical value. In addition, a control strategy is proposed to reduce the fluctuation of the cable force. By adjusting the input force of the first stage, the stability of the cable force transmission can be improved. Finally, numerical simulations and examples verify the correctness of the research content.

The results show that the model can accurately reflect the force transmission characteristics of the cable during the separation of the heat-shield and the lander. Through a novel control strategy, the stability of the cable force transmission is further improved. It is of great significance to the dynamic high-speed separation test of spacecraft.