This article presents a novel fixed-time safe-by-design control for uncertain active vehicle suspension systems (AVSSs) with matched/unmatched disturbances, high energy consumption, input saturations, and asymmetric time-varying constraints on both displacement/velocity. Several asymmetric time-varying barrier Lyapunov functions are carefully constructed to deal with displacement/velocity constraints under the fixed-time convergence framework. Furthermore, a new fixed-time auxiliary state system is proposed to compensate for the saturation effect. It is then rigorously demonstrated that the convergence time is independent of initial state conditions and both the displacement/velocity are always restricted within the asymmetric time-varying ranges. Importantly, by employing beneficial nonlinearities of a bioinspired X-shaped reference model, the burden of high control energy cost can be relaxed compared with traditional controllers. As far as we know, this should be the first attempt to achieve a fixed-time safe-by-design control for AVSSs, which simultaneously considers practical issues including meeting the safety requirements for input saturations and displacement/velocity, achieving fixed-time convergence, maintaining energy efficiency, and rejecting matched/unmatched disturbances. Experimental testing results validate the effectiveness, advantage, and feasibility of the proposed control algorithm, compared to other existing methods.

In this paper, a novel periodic sliding mode control method is designed for 4-DOF tower crane systems with unmatched disturbances as well as unknown/time-varying control directions. Specifically, the nonlinear disturbance observer is constructed to solve the unmatched uncertainties. The problems arising from unknown/time-varying control directions are tackled through the period sliding mode technique. Unlike most previous unknown control direction-related studies, the control coefficient is allowed to cross 0 in a continuous way. In addition, to improve the payload swing suppression and elimination performance, nonlinear terms involving payload swing information are elaborately injected into the control design. As far as we know, the designed periodic sliding mode control scheme provides the first control method for crane systems to successfully guarantee positioning as well as anti-swing performance in spite of unmatched disturbances and unknown control directions. The rigorous theoretical analysis is presented through Lyapunov techniques. Several simulations and experimental results are carried out to illustrate the merits of the designed periodic sliding mode control method.

Active vehicle suspension systems exhibit substantial vibration isolation capabilities, however, suffer from external disturbances, high energy consumption, risks of fault signals, limited transient performance, etc. In this paper, a predefined-time fault-tolerant control scheme is proposed for active suspensions to improve ride comfort and reliability, and enhance energy conservation. The reference X-dynamics together with a conditional disturbance cancellation scheme are developed to avoid the cancellation of beneficial nonlinearities and beneficial disturbances, respectively, which can reduce energy consumption without any optimization calculation or hardware alteration. Importantly, the error signals can converge to a predefined bound within the predefined time interval. Both the settling time and the residual bound can be arbitrarily user-defined, which are independent of initial states and control gains. Especially, to avoid singularity and alleviate chattering, a continuous piecewise function and a quadratic fraction inequality are constructed. The utilization of the proposed predefined-time fault-tolerant control facilitates satisfactory ride comfort with low energy cost. Experimental results are presented to validate the superior control performance of the designed control scheme.