Design and control strategy of gravity compensation system for rigid suspension-type astronauts operation training system

To simulate low- and micro-gravity environments crucial for astronaut training and space equipment motion control testing, achieving precise gravity compensation control of target object must be achieved to replicate the gravity characteristics of the target environment. Current suspension-type gravity compensation devices typically utilize single-cable or multi-cable driving mechanisms to replicate the gravitational conditions of outer space compared to the Earth’s surface. While effective in mimicking extraterrestrial gravity characteristics, cable-driven systems face challenges due to their inherent low-stiffness and variable-stiffness properties, especially in dynamically moving environments and in the presence of significant external disturbances. To address these challenges, a rigid suspension-type astronaut operation training system (RSAOTS) was developed. This system incorporated a constant-tension suspension composite control strategy aimed at enhancing gravity compensation accuracy by minimizing additional interference forces, thereby optimizing operational training effectiveness. An improved Stribeck friction compensation model was integrated to mitigate the impact of nonlinear friction on gravity compensation accuracy. Additionally, models for inertial force compensation and an Extended Disturbance Observer (EDO) were devised. The inertial force model estimates and compensates for inertial effects within the suspension system, while the EDO estimates and compensates for lumped disturbances in force loading. Further enhancing control precision, an admittance compensator calculates and compensates for loading force errors based on motion discrepancies, thereby refining simulated motion accuracy within the suspension system. Dynamic operational experiments were conducted to validate the feasibility of simulating zero-gravity conditions using the suspension system. The composite control strategy proposed in this study effectively reduces additional interference forces and improves force control accuracy, demonstrating promising results for simulating low- and micro-gravity operations.