This paper presents a safe control applied to a reaction wheel pendulum, assuring that the system satisfies stability objectives and safety constraints. Safety constraints are specified in terms of a set invariance and verified through control barrier functions (CBFs). The existence of a CBF satisfying specific conditions implies set invariance. The control framework considered unifies stability objectives, expressed as a nominal control law, and safety constraints, expressed as a CBF, through quadratic programming (QP). The work focuses on safety; thus, the nominal control law applied was a simple linear quadratic regulator (LQR). The safety constraint is considered to guarantee that the pendulum angular position never exceeds a predetermined value. The control framework was applied and analyzed considering continuous-time and discrete-time situations. The results from numerical simulations and experimental tests indicate that the pendulum is well stabilized while satisfying a safety constraint when forced to leave the safe set.
This article presents an improved method of obtaining lateral stability regions for road vehicles, considering the influence of steering angle, center of gravity, longitudinal speed, and tire-road friction coefficient on the vehicle dynamics. Comprehensive stability regions are obtained for a wide range of such parameters. Moreover, conservative stability regions are proposed, in the case of control applications that demand robust or safety-critical control actions. Next, a steering-angle-dependent region is used to implement a safety-critical electronic stability control system with active front steering as actuation. The resulting control system extends safety-critical control based on control-dependent barrier functions, introducing a control-dependent Lyapunov function to improve its steady-state behavior. Finally, we identify and propose workarounds for problems that arise from the number of inputs being less than the dimension of the desired safe set. The conservative stability regions and the extended safety-critical control system are validated by means of simulation results based on a nonlinear lateral stability model. INDEX TERMSActive front steering, control barrier function, electronic stability control, safety-critical control, vehicle lateral stability, vehicle stability control.
In this work we present a study concerning the modeling and control of two cooperative mobile manipulators for transport and manipulation of payloads. The advantages of such system can be summarized by the general system capacities in terms of size, weight and shape of payload to be transported, intricate moves and maneuvers and a wide range of applications. The study has an emphasis in the motion modeling and control of the system. The system is nonlinear and cannot be controlled by traditional linear control techniques. The motion is divided in the transport phase and the manipulation phase. In the transport phase, two mobile platforms carry the payload in a trajectory controlling the driving wheels in a formation control and in the manipulation phase, two manipulators carries the payload in a trajectory controlling the revolute joints. The control strategy proposed for the transport phase is the leader-follower with SDRE (State-Dependent Riccati Equation) method applied on formation control and the control strategies proposed for the manipulation phase are the SDRE method and the Variable Structure with Sliding Mode method. Simulation results with the software Matlab show the efficiency of the control strategies.
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