Adaptive Sliding Mode Control for an Active Gravity Offload System

In this paper, an adaptive sliding mode controller is designed for an active gravity offload system (AGOS). The system is consisted of a suspension structure, a buffer, a universal joint, a gantry robot, a tilt sensor, a tension sensor. The object is attached to the system through the suspension structure. The suspension structure is mounted on the buffer. The buffer is connected to the gantry robot through the universal joint and the tension sensor. The gantry robot can provide the object three dimensional space movement. The buffer and the gantry robot are utilized to simulate a variable gravity field. The suspension structure is used to guarantee the object to rotate freely. The system dynamics model is given based on Lagrange equation. Then an adaptive sliding mode controller is proposed considering the control input uncertainties, system uncertainties and external disturbances. The upper bounds of these uncertainties and disturbances are not required. The Lyapunov theory is utilized to verify the stability of the controller. Simulation results show the effectiveness of the proposed control strategy.