Vibration Control Of Flexible Space Structures With Active Tendons

The vibration control of the flexible space structure (FSS) is an important field in aerospace research. This paper focuses in exploiting the potential of the cables in the structures, in which the cable acts as active tendons, and researches on the feasibility of the active tendons to suppress the vibration of the FSS by both analytical and experimental approaches, and analyzes the stability of the active tendon in vibration suppression.First, the FSS with cables is introduced systematically. The feasibility of substituting active tendon for some existing cables on the FSS is discussed. The controllability grammian factor is adopted to quantitatively evaluate the controllability of the active tendons. The generic spacecraft model with a central rigid body and two flexible appendages is used to study the proposed method. Four installation methods of active cables are introduced and the controllability grammian factors are used to determine the optimal one.Non-preloaded tendons are adopted to attenuate the vibration of the FSS. Non-preloaded tendons do not deteriorate the configuration of the FSS, but the non-preloaded tendon, which can only provide pulling force, is a unilateral non-linearity actuator. In addition, the force saturation property caused by limited power of the controller adds the complexity to the controller design. As a result, a piecewise cost function is introduced to derive the optimal control law, and the stability of the control law with the acceleration feedback is discussed. The verification experiment on a pneumatic suspension table demonstrates the effectiveness of the proposed non-preloaded tendon and the control law for vibration suppression of flexible spacecraft, though the actuator can only work in half a vibration cycle due to its unilateral character.In order to control the vibrations of complex FSS with active tendon, the force on the preloaded tendon of the FSS is adopted to act as feedback signals and the tip movement of the active tendon is used to active displacement. A proportional-integral force feedback algorithm and a differential force feedback control algorithm are presented to increase the damping of the FSS. The two control algorithms, which require no structure model, can provide high damping ratio for the space structure. The stability of the control system is then shown. The simulation results on the structure similar to JPL-MPI demonstrate the effectiveness of the proposed algorithms for vibration control of the space structure.The active tendon has excellent performance for the vibration suppression of the FSS. But the time-varying force on the cables may cause self-excitation vibration, which will deteriorate the effectiveness of the control system. Therefore, the stability of the active tendon should be evaluated before controller design. The governing equation of the cable is derived to discuss the analytical relationship between the stable region and the physical parameters of the tendon by the method of strained parameters. The absolute nodal co-ordinate formation finite element method (FEM) is adopted to verify the stable region derived from the above analytical method. The simulation results of the FEM show that the analytical result can be used to direct the design of the active tendon to avoid the instability.