Fixed-time disturbance observer based fixed-time back-stepping control for an air-breathing hypersonic vehicle

This paper proposes a fixed-time backstepping control scheme based on fixed-time disturbance observer for flexible air-breathing hypersonic vehicles. The backstepping control is combined with the fixed-time control technique to achieve fixed-time convergence. A fixed-time super-twisting disturbance observer, which is convergent independently of initial conditions, is employed to estimate and compensate the uncertainties and flexible effects in tracking process. A nonlinear first-order filter is adopted to avoid the “explosion of complexity” problem that arises in traditional backstepping, and to guarantee overall fixed-time stability. The closed-loop system is proven to be semi-globally uniformly ultimately fixed-time bounded via Lyapunov analysis. Simulation results are given to demonstrate the effectiveness of the proposed scheme.     

Proposal of disturbance-compensating and energy-saving control method of air turbine spindle and evaluation of its energy consumption

This paper introduces a disturbance-compensating and energy-saving control method of an air turbine spindle equipped with a rotation control system designed for use in ultra-precision milling. As one of the key components, our proposed pneumatic regulating device, called a high-precision quick-response pneumatic pressure regulator (HPQR), is used to control the air supply pressure of the air turbine spindle precisely and quickly. The rotation feedback control system including the HPQR and a disturbance force observer, which avoids changes of rotation speed due to disturbance forces applied to the air turbine spindle, is explained. In addition, a pneumatic energy assessment method using a device called an “air power meter” is explained. The effectiveness of the proposed method is demonstrated through the experimental results.     

New variable gain super-twisting sliding mode observer for sensorless vector control of nonsinusoidal back-EMF PMSM

This paper presents a new discrete-time super-twisting sliding mode observer with variable gains for sensorless nonsinusoidal vector control of permanent magnet synchronous motors. This observer is adopted to estimate the back electromotive forces (back-EMF) that are required for the rotor speed estimation and for the nonsinusoidal vector control. In addition, their gains are time-varying to minimize the chattering. So, they are adjusted based on internal states of the super-twisting algorithm. The stability analysis is investigated from the Lyapunov theory for discrete-time systems. Finally, simulation and experimental results are presented to demonstrate the good performance and the effectiveness of the proposed observer.     

Prediction of acceleration length in turbulent gas–solid flows

CFD investigation for gas–solid flows in a horizontal pipe was performed using Euler–Euler approach or two-fluid model and accounting for four-way coupling. Calibration of the numerical model is obtained by confirming the numerical predictions with published experimental data. Based upon the axial profiles of the pressure gradient, the authors investigated the acceleration length for different particle properties and loadings. It is found that acceleration length increases generally with increasing particulate loading and/or decreasing gas phase mean flow velocity. However, the variations of acceleration length with particle diameter are quite different under different operating conditions. Finally, an empirical correlation for acceleration length (L_a) is proposed, which contains two terms: the first-term matches with the entrance length for gas only flow; whereas the second term is regarded as the enhancement due to addition of solids to gas flow. The accuracy of the correlation is approximately ±11%.     

Autonomous dynamic displacement estimation from data fusion of acceleration and intermittent displacement measurements

Addressing the importance of displacement measurement of structural responses in the field of structural health monitoring, this paper presents an autonomous algorithm for dynamic displacement estimation from acceleration integration fused with displacement data intermittently measured. The presented acceleration integration algorithm of multi-rate Kalman filtering distinguishes itself from the past study in the literature by explicitly considering acceleration measurement bias. Furthermore, the algorithm is formulated by unique state definition of integration errors and error dynamics system modeling. To showcase performance of the algorithm, a series of laboratory dynamic experiments for measuring structural responses of acceleration and displacement are conducted. Improved results are demonstrated through comparison between the proposed and past study.     

A virtual yaw rate sensor for articulated vehicles featuring novel electro-hydraulic steer-by-wire technology

Steer-by-wire technologies remain under rigorous research and development given the advantages that they offer over their traditional counterparts. The spectrum of steering systems encompasses applications in the automotive, construction, agricultural, and aerospace industries, to name a few.An original electro-hydraulic steer-by-wire technology based on pump displacement control actuation, an energy efficient alternative to conventional valve control, has been previously proposed by the authors. The new concept was validated and implemented on an articulated steering prototype test vehicle, and resulted in significant fuel savings and machine efficiency increase. This paper investigates the notion of virtual sensing relative to estimating the vehicle׳s yaw rate by only measuring the articulation angle and vehicle speed. Virtual sensing is a promising concept for yaw stability control and is an attractive option for vehicle manufactures as it reduces sensor cost, maintenance, and machine downtime. The designed yaw rate sensor is validated in simulation as well as on a test vehicle by devising appropriate steering maneuvers.     

A weighted variable gain super-twisting observer for the estimation of kinetic rates in biological systems

The knowledge of kinetic reaction rates is important for monitoring and controlling biotechnological processes. However, the lack of on-line sensors for this purpose and the inherent problems with numerical differentiation make observers indispensable. In this work, we propose the use of a weighted variable gain super-twisting observer (WVGSTO), applicable to a class of second-order nonlinear systems that include a measurable weight on the unmeasured variable and the possibility of bounding the perturbations with measurable functions. This estimation method is illustrated with an academic example and then applied to a fed-batch bioprocess.     

A geometric approach for adaptive estimation of unknown growth kinetics in bioreactors

This paper proposes a new approach for the estimation of unknown and time-varying specific growth rate in fed-batch bioprocess. A novel adaptive estimation technique based on the concept of invariant manifold is proposed as an effective approach to estimate growth kinetic parameters. An asymptotic nonlinear observer is used to provide simultaneous on-line estimation of biomass concentration and growth kinetic. The method is easy to implement and requires only one tuning parameter. The effectiveness of the proposed algorithm is illustrated with representative bioreactor simulation examples.