Research On Suspended Low Gravity Simulation System

With the increasing frequency of lunar activities, the space missions have become diverse, such as astronauts walking on the moon, lunar rover detectors carrying out exploration activities on the lunar ground, construction and maintenance of space stations. Due to the harsh natural environment of outer space, these tasks that are easy to accomplish on earth become extremely difficult on the moon. Among the many influencing factors, the effect of low gravity on astronauts and detectors can not be ignored. The low gravity environment on the moon will seriously affect the astronauts walking and operation, as well as a series of physical and psychological activities. At the same time, the impact of gravity field changes on lunar rover, space robots and other mechanical devices is obvious. Due to the different power input and output, if not rigorously designed, these mechanical devices may be directly damaged on the moon.So, before landing on the moon,strict low-gravity simulation test is essential. Through the low gravity simulation test, we can train astronauts walking skills in low gravity environment, and can test the design rationality of lunar rovers and space robots.In this paper, a simple low-gravity simulation system has been designed, which mainly includes the constant tension system. And the parameters of the motor, rope and reel have been selected. The SVPWM control of the permanent magnet synchronous motor selected by the constant tension system has been simulated. At the same time, the mathematical model of the permanent magnet synchronous motor vector control with load has been established, and the system speed control model has been obtained. For the constant tension system, a phase advance position controller has been designed.Using the force/position control strategy, a PI force controller has been designed and the low gravity simulation in Simulink has been implemented. The model of the low gravity simulation system has been simplified, and the rope has been separated into several quantity-spring-damping unit. Then, the simplified system has been modeled and simulated. The influence of the rope length, damping and stiffness parameters on the system performance has been studied, getting the basis of election of the low gravity simulation test rope. This paper has briefly studied the control strategy of the horizontal servo system, and put forward the combination of a PD controller and a Lyapunov nonlinear controller to compensate the horizontal displacement deviation while suppressing the swing energy of the system and keeping the system stable.