Adaptive super-twisting observer for fault reconstruction in electro-hydraulic systems

An adaptive-gain super-twisting sliding mode observer is proposed for fault reconstruction in electro-hydraulic servo systems (EHSS) receiving bounded perturbations with unknown bounds. The objective is to address challenging problems in classic sliding mode observers: chattering effect, conservatism of observer gains, strong condition on the distribution of faults and uncertainties. In this paper, the proposed super-twisting sliding mode observer relaxes the condition on the distribution of uncertainties and faults, and the gain adaptation law leads to eliminate observer gain overestimation and attenuate chattering effects. After using the equivalent output-error-injection feature of sliding mode techniques, a fault reconstruction strategy is proposed. The experimental results are presented, confirming the effectiveness of the proposed adaptive super-twisting observer for precise fault reconstruction in electro-hydraulic servo systems.Comment: Final versio

Transverse and longitudinal dynamic modeling of bimorph piezoelectric actuators with investigating the effect of vibrational modes

Bimorph piezoelectric cantilevered (BPC) actuators have recently received a great deal of attention in a variety of micro-electromechanical systems (MEMS) applications. Dynamic modeling of such actuators needs to be improved in order to enhance the control performance. Previous works have usually taken transverse vibration into account without considering longitudinal vibration. This paper presents a comprehensive modeling for a set of transverse and longitudinal vibration equations for piezoelectric cantilevered actuators. In addition, dynamic behavior and exact non-minimum phase region along BPC is derived by analyzing first three vibrational modes. A simulation study is propounded to better analyze the system dynamic behavior. Finally, an experimental setup is developed to verify the proposed dynamic model. The modal frequency response of the system for the first three modes, obtained from the proposed model, is compared with those obtained from the experiment and a good consistency between them confirms the validity of the proposed dynamic model.<br /

Robust Adaptive Control of a Micro Telemanipulation System Using Sliding Mode-Based Force Estimation

Abstract-Piezoelectric actuators are widely used in micro manipulation applications. However, hysteresis nonlinearity limits the accuracy of these actuators. This paper presents a novel approach for utilizing a piezoelectric nano-stage as the slave manipulator of a teleoperation system based on a sliding mode controller. The Prandtl-Ishlinskii (PI) model is used to model actuator hysteresis in feedforward scheme to cancel out this nonlinearity. The presented approach requires full state and force measurements at both the master and slave sides. Such a system is costly and also difficult to implement. Therefore, sliding mode unknown input observer (UIO) is proposed for full state and force estimations. Furthermore, the effects of uncertainties in the constant parameters on the estimated external forces should be eliminated. So, a robust adaptive controller is proposed and its stability is guaranteed through the Lyapunov criterion. Performance of the proposed control architecture is verified through experiments

Performance evaluation of services quality in higher education institutions using modified SERVQUAL approach with grey analytic hierarchy process (G-AHP) and multilevel grey evaluation

In today’s climate of fierce competition, there is a necessity to pay especial attention on customer demands either in manufacturing or service sector. Managers in service sector are under pressure in terms of environmental factors, they focus on customers’ satisfaction and this has led to the continuous improvement in the performance of service organizations. Meanwhile, customers’ expectations should be properly understood and measured. There have been various efforts to measure the quality of services using the SERVQUAL model. In this study, we try to investigate the concepts and factors influencing the quality of services according to modified SERVQUAL model and then utilize the proposed model of Grey Analytic Hierarchy Process (G-AHP) and Multilevel Grey Evaluation in order to evaluate the quality of services in the framework of Grey Systems Theory (GST). In order to propose our method, we will conduct a case study of the performance of service quality in higher education institutions of Isfahan-Iran

Robust control of a piezoelectric stage under thermal and external load disturbances

Piezoelectric actuators are widely used inmicromanipulation tasks such as Atomic Force Microscopy andCell Manipulation. However, the hysteresis nonlinearity andthe creep reduce their fidelity and cause difficulties in themicromanipulation control procedure. Besides, variation oftemperature and external loads could change the modeparameters identified for the piezo actuator. In this paper, anovel feedforward-feedback controller is proposed. ThePrandtl-Ishlinskii model is utilized to linearize the actuatorhysteresis in feedforward scheme and ad sliding mode based impedance control with perturbation estimation is used tocancel out the thermal and external load disturbances infeedback scheme. The efficiency of the proposed controller is verified by experiments.</p

Robust control of a piezoelectric stage under thermal and external load disturbances

Piezoelectric actuators are widely used inmicromanipulation tasks such as Atomic Force Microscopy andCell Manipulation. However, the hysteresis nonlinearity andthe creep reduce their fidelity and cause difficulties in themicromanipulation control procedure. Besides, variation oftemperature and external loads could change the modeparameters identified for the piezo actuator. In this paper, anovel feedforward-feedback controller is proposed. ThePrandtl-Ishlinskii model is utilized to linearize the actuatorhysteresis in feedforward scheme and ad sliding mode based impedance control with perturbation estimation is used tocancel out the thermal and external load disturbances infeedback scheme. The efficiency of the proposed controller is verified by experiments.</p