Quantum cascade lasers (QCLs) are semiconductor emitters that cover the mid-infrared (MIR) wavelength range [1] . Surface-emitting semiconductor lasers can be easily arrayed, and their use in sensing applications has increased dramatically in recent years. In addition, compared to the edge-emitting type, there is no cleavage process that lowers the yield, and the inspection can be performed on the wafer, surface-emitting lasers are excellent in productivity [2], [3] . QCLs emit TM-polarized light from the principle of light emission, surface-emitting lasers can be realized by using photonic crystals (PCs). Surface emission of QCL was realized with PC [4]–[6] . We fabricated quantum cascade lasers with PC of low-symmetric pillars as unit cell, and evaluated and analysed the oscillation characteristics. An active layer composed of InGaAs / InAlAs strained quantum wells designed for the oscillation wavelength of 4 μm was grown by molecular beam epitaxial growth, and a PC composed of InGaAs / InP was formed by buried regrowth (Fig. 1(a)). The PC is a low-symmetric pentagonal prism shape. Low-symmetry allows lower oscillation threshold for modes that allow radiation in the direction normal to the surface. Fig. 1(b) shows the characteristic of current-light output power of the surface-emitting QCL driven by a pulse current at 77K. Fig. 1(c) shows a far-field image. The light intensity is unimodal, and it can be seen that only the mode that permits radiation in the plane direction oscillates. A very narrow emission angle of less than 1°, which is characteristic of surface-emitting lasers with a large emission area, has been observed.
We propose a novel method for estimating the initial position and achieving low-speed sensorless control of synchronous motors based on system identification theory. We derive mathematical models that consider magnetic saturation, and use this model for position estimation. The proposed method requires neither any band-pass filters nor motor parameters, and it can be applied to all kinds of synchronous motors without any tuning. Polarity detection of the magnetic pole can be also determined simultaneously with position estimation, making extra signals for polarity detection unnecessary. The proposed estimation method is verified experimentally.
A vector control system of an induction motor is proposed to suppress influence of iron loss. It is pointed out that the rotor flux estimator contributes more to torque control linearity than the current controller. Therefore, it is proposed that a rotor flux observer which can suppress the influence of some parameter deviations, (especially that of rotor resistance), can be applied to decrease the sensitivity to iron loss resistance. Finally, some experimental results of improved torque control linearity are shown to verify effectiveness of the proposed system.
In the field of robotics, many researchers have studied the representation and analysis of an automatic assembly system. In previous research, however, no control-theoretic ideas for the assembly system have been found. In this paper, the authors study a closed-loop desired marking control problem for the automatic assembly system using the supervisory control technique. First, the authors represent the assembly system with a Petri net. Since the assembly Petri net has a "tree structure", the authors show that the assembly Petri net has some formal linguistic properties. Based on the properties, the authors clarify that the solvability of the desired marking control problem depends only on the controllability of a control object, and that one can construct the supervisor for the assembly Petri net with a finite automata. Finally, the authors discuss the supervisor reduction technique and give two examples.< >
Recently, synchronous reluctance motors (SynRMs) have attracted study because of their favorable properties, including limited thermal expansion of the shaft due to low heat generation by the rotor, the ability to drive at high velocity, a low degree of torque ripple and an absence of demagnetization problems. Sensorless control of SynRMs is now desired, and several methods have been proposed. These methods, however, have difficulties at low speed when the voltage signal necessary to estimate rotor position is very small. The authors have proposed a new position estimation method using high-frequency extended e.m.f. (EEMF) in which high-frequency voltage and current are calculated using a disturbance observer. Simulations have shown the new method to be very useful. This paper discusses the ability of the new method to estimate rotor position when the rotor is at a standstill, as demonstrated through experiments.
A stability analysis of a digital current controller for a PWM (pulsewidth-modulation) inverter using a neural network is described. The Lyapunov method is used for the analysis. The stability condition for the learning rate of the neural network is clarified. Simulations and experiments done to verify the analytical results show that the neural network can stably compensate a delay necessary for calculation of the digital controller itself and tune gains of the current controller to optimal values.< >
The authors describe the design method for a robust adaptive sliding observer which realizes speed-sensorless field-oriented vector control of AC motor drives. The speed-sensorless field oriented vector control system using the adaptive sliding observer was implemented. The basic characteristics of the proposed system and the design method against parameter deviation were studied experimentally. In the present system, the steady state error of the speed control was about 0.3% and the settling time was about 100 ms. The proposed system had good characteristics of speed control even in a low-speed region. The pole assignment, considering H/sub infinity / norm of the transfer function from disturbances, realized good characteristics of the speed-sensorless field-oriented vector control even with parameter deviations.< >
An ultrasonic motor is a promising actuator for robots since it has a simple construction, high response, and high torque at low speeds. This paper proposes a robot hand using vibration-type ultrasonic motors as the fingers instead of moving elements. This robot hand with three fingers can simultaneously grasp and rotate a cylindrical body. The driving characteristics of the robot hand were examined experimentally under various conditions. It was confirmed that high torque was obtained when the optimum contact angle and contact force of the ultrasonic motors were used. The reduction of the output torque is small even when the diameter of the rotational body deviates from the designed value.
