Safety issue is great concern for rehabilitation robots that are expected to contribute to future aging society. Appropriate compliance is required for their joints. However, combination of servomotors and high-ratio gears, such as harmonic gears makes the joint of robots nonbackdrivable. The nonbackdrivability causes lack of adaptability and safety. On the other hand, Conventional direct-drive systems, including linear motors, are relatively big for such application. This paper presents development and analysis of compact high backdrivable direct-drive linear actuator. The motor consists of a helical structure stator and mover. The mover does not contact the stator and moves helically in the stator under a proper magnetic levitation control. Thus, the motor realizes direct drive motion without mechanical gears. Decoupling control is proposed and integrated with disturbance observer to achieve robustness against model uncertainties and input disturbance. The main contribution of this paper is to experimentally realize the direct-drive feature of the helical motor.

Enhancing the performance of the voltage source inverters (VSIs) without changing the hardware structure has recently acquired an increased amount of interest. In this study, an optimization algorithm, enhancing the quality of the output power and the efficiency of three-phase grid connected VSIs is proposed. Towards that end, the proposed algorithm varies the switching frequency (f sw ) to maintain the best balance between switching losses of the insulated-gate-bipolar-transistor (IGBT) power module as well as the output power quality under all loading conditions, including the ambient temperature effect. Since there is a contradiction with these two measures in relation to the switching frequency, the theory of multi-objective optimization is employed. The proposed algorithm is executed on the platform of Altera ® DE2-115 field-programmable-gate-array (FPGA) in which the optimal value of the switching frequency is determined online without the need for heavy offline calculations and/or lookup tables. With adopting the proposed algorithm, there is an improvement in the VSI efficiency without degrading the output power quality. Therefore, the proposed algorithm enhances the lifetime of the IGBT power module because of reduced variations in the module's junction temperature. An experimental prototype is built, and experimental tests are conducted for the verification of the viability of the proposed algorithm.

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In this paper, modeling and control of spiral motor is proposed. The voltage equation and motion equation of the spiral motor is proposed. Based on this modeling, control system for the spiral motor is proposed. The proposed controller consists of three parts; the first part is PI current controller with back EMF compensation specialized for spiral motor, the second part is disturbance observer based PD controller for linear and gap motion interacting each other, and the third part is zero-power controller for equilibrium fluctuation of gap displacement. It is confirmed that the proposed controller achieves independent linear position and gap control simultaneously.

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In this paper, we introduce the control of the strange attractor, chaos. Because of the importance of controlling undesirable behavior in systems. researchers are investigating the use of linear and nonlinear controllers, either to remove such oscillations (in power systems) or to match two chaotic systems (in secure communications). The idea of using the fuzzy logic concept for controlling chaotic behavior is presented. There are two good reasons for using fulzy control: first, there is no mathematical model available for the process; secondly. it can satisfy nonlinear control that can be developed empirically. without complicated mathematics. The two systems are well-known models so the first reason is not a big problem. and we can take advantage of the second reason.

Many reduced-switch-count (RSC) inverter topologies have been proposed in the literature. As the number of switches required to produce a set of voltages in RSC inverters are less than that in conventional inverter, as a result utilizing RSC inverters in a certain system reduces its size and cost. In this paper, a novel RSC shared inverter topology consisting of fifteen switches and capable of driving four three-phase AC-loads independently is proposed and experimentally verified. A carrier-based pulse width modulation (PWM) technique that employs the zero-sequence-signal injection principle is developed to drive the proposed inverter along with adequate DC voltage bus utilization between the shared loads for common frequency (CF) as well as different frequency (DF) modes. The structure and the principle of operation of the proposed inverter are introduced and intensively verified using simulation and field-programmable-gate-array (FPGA)-in-the-loop simulation under linear and nonlinear loads. Then, Inverter prototype was built and the proposed inverter has been verified experimentally. The experimental results verify the applicability of the proposed inverter and the employed PWM.

Purpose -To propose a new method for controlling the overhead crane systems based on the theory of fuzzy logic with a reduced number of rules than has appeared before in the literature. The proposed fuzzy logic controller (FLC) can be implemented to move the overhead crane along a desired path while ensuring that the payload is swing free at the end of the motion. Design/methodology/approach -In this study, a FLC that includes two rule bases, one for displacement control, the other for swing control, was designed and successfully implemented to move the overhead crane along a desired path while ensuring that the payload is swing free at the end of the motion. Findings -Control simulation results demonstrate that by using the proposed FLC, the overhead traveling crane smoothly moves to the destination in short time with small swing angle and almost no overshoot. Originality/value -This paper offers practical help to whom are working in controlling the transporting the payloads to the required position as fast and as accurately as possible without collision with other equipments. The proposed FLC can be implemented to move the overhead crane along a desired path while ensuring that the payload is swing free at the end of the motion.