Attitude control law design for moving mass control reentry vehicle based on sliding mode
Due to issues of aerodynamic ablation, complicated mechanical environment and serious nonlinear dynamics, the control system is difficult to achieve high accuracy. For nonlinear dynamics of moving mass control reentry vehicle, a design method based on sliding mode for pitch-yaw channel attitude control is proposed, which improves control accuracy and anti-disturbance capability. According to a reentry vehicle attitude control system, the pitch-yaw channel dynamic model of the nonlinear system is firstly given. Secondly, designed by using backstepping theory, a sliding mode controller with approach law is proposed. Besides, in order to reduce chattering of sliding mode control, an improved sliding mode controller is presented, in which relay characteristics is replaced with continuous functions. Finally, simulation results demonstrate the validity and feasibility.
Integrated Guidance and Control of Moving-Mass Actuated Kinetic Warheads
Abstract : Modeling, simulation, and integrated guidance-control of a kinetic warhead utilizing moving- mass actuators are discussed. Moving masses can be used in any speed range both in the atmosphere as well as outside it, as long as there is a force, either aerodynamic or propulsive, acting on the vehicle. Since they are contained entirely within the airframe geometric envelope, and because no mass expulsion is involved, moving-mass actuation technique offers significant advantages over conventional aerodynamic control surfaces and reaction control systems. The present research developed a high fidelity, nine degree-of-freedom simulation model of a kinetic warhead with three moving-mass actuators. This simulation model is used for actuator sizing and in the development of flight control systems. A software package for performing numerical feedback linearization technique is employed for the design of nonlinear flight control systems. Interception of non-maneuvering and weaving targets in both atmospheric and exo-atmospheric conditions are demonstrated.
Fabrication of PLLA/C3S Composite Membrane for the Prevention of Bone Cement Leakage
Kyphoplasty is an important treatment for stabilizing spine fractures due to osteoporosis. However, leakage of polymethyl-methacrylate (PMMA) bone cement during this procedure into the spinal canal has been reported to cause many adverse effects. In this study, we prepared an implantable membrane to serve as a barrier that avoids PMMA cement leakage during kyphoplasty procedures through a hybrid composite made of poly-l-lactic acid (PLLA) and tricalcium silicate (C3S), with the addition of C3S into PLLA matrix, showing enhanced mechanical and anti-degradation properties while keeping good cytocompatibility when compared to PLLA alone and most importantly, when this material design was applied under standardized PMMA cement injection conditions, no posterior wall leakage was observed after the kyphoplasty procedure in pig lumbar vertebral bone models. Testing results assess its effectiveness for clinical practice.