Yukinori Nakamura

Distributed power adjustment based on control theory for cognitive radio networks

In this paper, we propose two power adjustment methods for cognitive radio networks. In the first algorithm, the transmitter derives the transmission power with PID control in order to satisfy the QoS constraints in secondary networks. The derived transmission power is compared with a constraint condition in order to avoid the interference with primary networks, and then the actual transmission power is decided. Because the constraint condition affects the performance of our proposed method significantly, we propose an effective update algorithm. On the other hand, the second algorithm is based on model predictive control (MPC). In this method, the decision of transmission power is formulated as quadratic programming (QP) problem and the transmission power is derived directly with the constraint condition. We evaluate the performances of our proposed methods with simulation and compare the proposed methods with the distributed power control (DPC) method. In numerical examples, we show that our proposed methods are more effective than the existing method in some situations. We also prove analytically that the interference with primary networks can be avoided with probability one by using our proposed method if each transmitter has the information about every channel gain.

A phase stabilization method for unbalance vibration control of five-axes active magnetic bearing systems

As one of the problems of the rotary machine, unbalance vibration caused by the unbalance of the mass of the rotor, the electromagnetic force in the TMP, and the position of the AMB is well known. Peak-of-Gain Control (PGC) and Automatic Balancing System (ABS) have been reported as the compensation methods of the unbalance vibration, This paper considers the new compensation method for unbalance vibration of five-axes active magnetic bearing systems. The proposed Phase-Variable Control (PVC), which is a phase stabilization method, consists of the cascade connection of the PGC and ABS. By using this compensator, only the phase of a control system can be adjusted. It leads to the whirling suppression of a rotor. The performance of the proposed and conventional unbalance vibration compensators is compared by experiments on the rotational test of a turbo molecular pump.

Unbalance vibration control for active magnetic bearing using automatic balancing system and peak-of-gain control

This paper considers unbalance vibration for five-axes active magnetic bearing systems. To suppress the vibration, the automatic balancing system (ABS) and the peak-of-gain control (PGC) are utilized. By using the ABS (the PGC), the bearing stiffness at rotational frequency is increased (decreased). In previous works, implementation methods for these have not been presented fully. Thus, in this paper, we considered the implementation of the ABS and the PGC. Moreover, in the conventional PGC, the feedback gain must be tuned according to the rotational speed of the rotor. This results in the increase of tuning cost. In order to solve this problem, the structure of the PGC is improved. Practical advantages of the PGC/ABS are demonstrated by rotational tests of a turbo molecular pump.

Smith predictor-based time delay compensation for attitude control of pneumatic anti-vibration apparatuses with two degrees-of-freedom

Pneumatic anti-vibration apparatuses (AVAs), which have air springs, are needed for the precision positioning of wafer stages in lithography equipment. However, the difference of time delays in the response of the air springs causes the undesirable rotational motion of an isolated table. This paper considers the attitude control of the AVA including difference time delays. To avoid the rotation of the isolated table, a Smith predictor is employed. It is verified that this approach can be used for the AVAs with mode control, which is often used in vibration isolation systems for semiconductor manufacturing. The overshoot of the rotational angle of the isolated table can be further reduced by shaping the reference trajectory.

Pressure estimation of pneumatic anti-vibration apparatuses using an identity observer

This paper considers the parameter tuning of the identity observer and the implementation method of the estimated pressure feedback for a pneumatic anti-vibration apparatus. To tune the observers parameters efficiently, the number of parameters is reduced by equivalent transformation of the block diagram of the observer. The pole assignment of the observer is verified based on the time response of the position error. Moreover, by considering the saturation of output voltage of the driver circuit, estimation error is reduced. Experimental results show the effectiveness of the proposed method.

Switching control of an air type anti-vibration apparatus under earthquake ground motion

This paper presents the control method for the continuous operation of semiconductor exposure machines under earthquake ground motion. In our method, floor vibration feedforward control and relative acceleration feedback control are switched on or off, and the gain of the acceleration feedback controller is changed. The acceleration of the floor vibration, the relative displacement between the isolated table and the floor, and the difference of spectral intensity (SI) value are utilized as switching signals. By using the switching control strategy, effects of unknown earthquake can be compensated. The effectiveness of the proposed method is shown by simulation and experimental results.

Pneumatic stage positioning with model following control and PDD² control

This paper addresses the performance improvement of positioning for a pneumatic stage. In the positioning with proportional-derivative-double derivative (PDD²) control, the stiffness and damping of a control system can be easily adjusted. However, due to unknown parameter of a pneumatic system, there is a difficulty in achieving high repeatability of positioning. To solve this problem, model following control (MFC) is combined with the PDD² control. Since, by using the MFC, the pressure in a chamber can track the output of a desired model, the repeatability is improved under the condition that the parameter of pneumatic system is unknown. It is shown that the desired model of a first-order lag system is appropriate for the positioning of the pneumatic stage. Furthermore, the difference between MFC and disturbance observer is discussed. The effectiveness of the proposed approach is shown by experiments on positioning.

A design method of a mode control and an unbalance vibration control for five-axes active magnetic bearing systems

Mass unbalance of magnetically levitated rotors causes deteriorations of dynamic and static characteristics. To avoid this problem, it is necessary that mode matrices (i.e., a mode selection/distribution matrices) are adjusted appropriately. This is because these matrices are set based on the rotor’s centre of gravity and magnetic force coefficients of electromagnets. It takes long time to adjust the parameters of the mode matrices by trial and error. To design these parameters efficiently, we propose an adjustment method based on experimental analysis. Experimental results of step response show effectiveness of the proposed method. On the other hand, the eccentricity of the rotor causes unbalanced vibration, which is a common problem in rotating machinery. To suppress the vibration, automatic balancing system (ABS) and peak-of-gain control (PGC) are utilised. By using the ABS (the PGC), the bearing stiffness at rotational frequency is decreased (increased). In previous works, implementation methods for these have not been presented fully. Thus, in this paper, we considered the implementation of the ABS and the PGC. Moreover, practical advantages of the PGC/ABS are demonstrated by rotational tests of a turbo molecular pump.

Control of a pneumatic anti-vibration apparatus under long-period earthquake ground motion using SI value

This paper considers control of a pneumatic anti-vibration apparatus under long-period earthquake ground motion. To suppress effects of the earthquake, floor vibration feedforward and acceleration feedback controls are automatically stopped based on any floor vibration displacement. Next, to detect the long-period earthquake ground motion, this paper considers SI (Spectral Intensity) value. Performance of proposed method is evaluated by simulations using measured seismic waveforms.

Implementation of floor vibration feedforward using an absolute displacement sensor combined with acceleration PI feedback

In the field of vibration control of semiconductor exposure equipments, commercial accelerometers have been used as feedforward sensors of floor vibrations. In order to suppress direct motion i.e., disturbances against an isolated table, the equipments have air springs in anti-vibration apparatuses. Therefore, once integration was required to provide the floor vibration feedforward, even when we utilized an integral characteristic of the air spring. In this paper, an absolute displacement sensor is utilized instead of the accelerometers to detect velocity and displacement signals of the floor vibration, and these signals are directly fed back to a voice coil motor as feedforward signals. Then, we can implement the floor vibration feedforward without amplifications of the pink-noise in low frequency. Although the effects of the feedforward are generally investigated in frequency responses of transmissibility, we evaluate time responses. As a result, transmissions of the floor vibrations are successfully suppressed on the isolated table.