Applied Mechatronics: On Mitigating Disturbance Effects in MEMS Resonators Using Robust Nonsingular Terminal Sliding Mode Controllers

This investigation attempts to study a possible controller in improving the dynamic stability of capacitive microstructures through mitigating the effects of disturbances and uncertainties in their resultant dynamic behavior. Consequently, a nonsingular terminal sliding mode control strategy is suggested in this regard. The main features of this particular control strategy are its high response speed and its non-reliance on powerful controller forces. The stability of the controller was investigated using Lyapunov theory. For this purpose, a suitable Lyapunov function was introduced to prove the stability of a controller, and the singularity conditions and methods to overcome these conditions are presented. The achieved results proved the high capability of the applied technique in stabilizing of the microstructure as well as mitigating the effects of disturbances and uncertainties.

Fault-tolerant control of a rotary shape memory alloy actuator using a terminal sliding mode controller

This paper focuses on developing a Fault-tolerant control (FTC) method for a rotary Shape Memory Alloy (SMA) actuator against actuator faults. The SMA actuator uses a pair of SMA wires in the antagonistic configuration for rotating a pulley. A proposed Terminal Sliding Mode Controller (TSMC) is utilized to compensate for the effects of actuator faults and to guarantee acceptable tracking performance in the presence of faults. The developed closed-loop scheme is applied to both a simulated model of the actuator as well as a real actuator in an experimental setup and then, the performance is evaluated and compared with a Proportional (P) controller and a sliding mode controller. It is shown that the proposed scheme works well in both normal and faulty conditions. The experimental results indicate that TSMC has almost no steady-state error while both P and sliding mode controllers have a considerable error (about 20% relative error), in the presence of the actuator faults.

Robust fuzzy sliding mode controller for a skid-steered vehicle subjected to friction variations

Skid-steered vehicles (SSV) are gaining huge importance in the market due to their applications like construction, agricultural work, material handling etc. The accuracy of performing such tasks require a robust control algorithm. The design of such controller is very challenging task due to external disturbances caused by wheel-ground interaction and aerodynamic effects. This paper proposes robust fractional and integral order fuzzy sliding mode controllers (FSMC, FFSMC) for a skid-steered vehicles with varying coefficient of friction and a displaced center of gravity (CG). FFSMC controller reduces the outcome of forces generated as a result of ground tire interaction during skidding and friction variations. The proposed controllers are implemented for a four-wheel SSV under high-speed turning motion. A simulation environment is constructed by implementing the SSV dynamics with wheel-road model and the performance of the proposed algorithms is tested. The simulation test is conducted for a Pioneer-3AT (P-3AT) robot SSV vehicle with displaced CG and variable coefficient of tires friction. Simulation results demonstrate the efficiency of the proposed FFSMC algorithm in term of reduced state errors and minimum chattering. The proposed controller compensates the effect of different responses of the wheels generated as a result of variable CG. The chattering phenomenon generated by conventional SMCs is also minimized by fuzzy tuning approach.

Gas Turbine Aerodynamics Improvement Via a Design of Intelligent Fractional Control

Gas turbines are complex processes characterized by the instability and uncertainty of various sources. The range of useful operating in an axial compressor which is part of a turbine gas is limited by aerodynamic instabilities that are surge and rotating stall. This paper presents two intelligent fractional order sliding mode controllers. At first, a robust sliding fractional surface form is proposed to deal with hazardous phenomena which limit compression systems performance, and speed transitions, which can lead to temporary stall development, pressure drop at the output, degrade the effective operation of compressors and consequently gas turbines. Second, to reduce the chattering/fluctuation in control, a fuzzy logic and finite time criterion are used as switching control at the reaching phase in the sliding mode control. Additionally, the controller gains are obtained by offline multi-objective Particle swarm optimization (MOPSO) search. Finally, the surge and rotating stall of a Variable Speed Axial Compressor (VSAC) in a gas turbine are investigated under the system nonlinearities and also in presence of an external disturbance and perturbations. The simulation results signify the performance of the two MOPSO-based fractional sliding mode controllers.