Jiacai Huang

This article addresses the problem of global stabilisation using state feedback for a kind of uncertain non-holonomic systems in chained form. Two distinct characteristics of this study are that the considered system suffers from the input-quantised actuator, and the system states are expected to converge to zero in prescribed finite time. To address these, a time-scale transformation, that can change the original stabilisation into the finite-time stabilisation of the transformed one, is first introduced. Then, under the new framework of equivalent transformation, a quantised state feedback controller that achieves of the performance requirements is developed with the aid of the recursive technique. Finally, simulation results of a unicycle-type mobile robot are provided to confirm the efficacy of the proposed approach.

This brief reports the prescribed-time stabilization (PST) problem for a class of uncertain planar nonlinear systems with output constraints. To handle the obstacle caused by the output constraints, a tan-type Barrier Lyapunov Function (BLF) that equates to the classical one for unconstrained systems is exploited. By suitably introducing the time-varying function into the virtual (actual) controllers rather than conventionally to scale the coordinate transformations, a switched, non-scaling design scheme for state feedback is developed to ensure that the origin of the resulting closed-loop system (CLS) is prescribed-time stable without disobeying the constraints. The novelty of the proposed control strategy is that it solves the computationally singular problem effectively and leads to a simpler controller in comparison with the traditional scaling design. Finally, the appealing performance of the proposed scheme is illustrated by simulation.

A novel 6-degree-of-freedom (6-DOF) parallel robot driven by six novel linear motors is designed and controlled in this paper. Detailed structures of linear motors are illustrated. A control strategy based on kinematics of the 6-DOF parallel robot is used, and six linear motors are controlled to track their own desired trajectories under a designed fractional-order active disturbance rejection controller (FOADRC). Compared with the normal ADRC, two desired trajectories and three different working situations of a linear motor are simulated to show good performances of the FOADRC. Experimental results show that six linear motors can track their own desired trajectories accurately under payloads and disturbances, and the novel 6-DOF parallel robot can be controlled well.

In the process of extrapolating a lifetime distribution function under normal storage conditions through nonlinear accelerated degradation data, time indexes under the normal storage conditions are usually set to the mean value of time indexes under various accelerated stresses. However, minor differences in time indexes may lead to great changes in the assessment results. For such a problem, an accelerated degradation model of a nonlinear Wiener process based on a fixed time index is established first and meanwhile, the impact of the measurement error is considered. Then, the probability density function is normalized, and multiple unknown parameters are estimated by using fminsearch function in MATLAB and multiple iterations. Finally, the model is validated by accelerated degradation test data of accelerometers and the O-type rubber sealing rings. The results show that there is a difference of 30,710 h for accelerometers between the mean time to failure under normal storage conditions obtained by the proposed method and the mean time to failure when the time indexes are the mean value of those under various accelerated stresses, and the main cause of the difference is compared and analyzed. A similar phenomenon is observed in the case study of O-type rubber sealing rings.

A new robust fractional‐order sliding mode controller (FOSMC) is proposed for the position control of a permanent magnet synchronous motor (PMSM). The sliding mode controller (SMC), which is insensitive to uncertainties and load disturbances, is studied widely in the application of PMSM drive. In the existing SMC method, the sliding surface is usually designed based on the integer‐order integration or differentiation of the state variables, while in this proposed robust FOSMC algorithm, the sliding surface is designed based on the fractional‐order calculus of the state variables. In fact, the conventional SMC method can be seen as a special case of the proposed FOSMC method. The performance and robustness of the proposed method are analyzed and tested for nonlinear load torque disturbances, and simulation results show that the proposed algorithm is more robust and effective than the conventional SMC method.