Language：Japanese   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electrical Engineers of Japan  

This paper considers data-driven type generalized minimum variance control (GMVC) for p-inputs/q-outputs (p > q) multivariable systems with static nonlinearity. In the proposed approach, an autoencoder, which can extract the feature of input data, is used. First, an encoder converts input data with p dimensions into that with q dimensions. Then, a GMV controller is designed by using the dimension-reduced input data. Finally, the nonlinearity of a plant is compensated by a decoder, which reconstructs the input data with p dimensions. The effectiveness of the presented approach is evaluated using a numerical example.

DOI： 10.1541/ieejeiss.143.305

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/icmech.2019.8722927

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DOI： 10.1109/SII.2017.8279259

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical Engineers of Japan  

This paper considers the positioning of a pneumatic stage. To achieve high precision positioning under different length of pipe, which connects servo valves and cylinders, a pneumatic system is divided into two subsystems. In this situation, model following control (MFC) is employed so as to compensate effects of unknown parameter of the pneumatic system. Experiments demonstrate that, by using the MFC, the repeatability of positioning is improved.

DOI： 10.1541/ieejeiss.137.273

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Language：Japanese   Publisher：The Japan Joint Automatic Control Conference  

DOI： 10.11511/jacc.60.0_1628

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Model Predictive Control is an effective control method for nonlinear plants with constraints. However, application to large-scale systems and/or processes that require high sampling rate is quite challenging because of the heavy computation. Here we consider MPC approach for the cooling process of hot-rolled strip having 3D thermal distribution. To solve this large-scale problem, we propose a method to change the resolution of the model dynamically according to the uniformity of the thermal distributions in the directions of interest. Combined with a hierarchical control strategy to flatten the thermal distribution in a certain direction, one can balance the computational load across the cooling process.

DOI： 10.1109/IECON.2016.7793811

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This paper considers the applicability of cascade-type proportional-integral-sinusoidal (PIS) control for suppression of flow disturbance to the pneumatic vibration isolator. In the PIS control, a sinusoidal compensator (S compensator) is employed for the suppression of periodic disturbance. However, due to the phase lag of this compensator, a PIS control system is destabilized. It is shown that even if gains of PI compensator are retuned, the control system cannot be stabilized. Moreover, it is also shown that, by using the cascade-type PIS and phase-lead control, the flow disturbance can be suppressed. Experimental results validate the effectiveness of proposed approach.

DOI： 10.1109/IECON.2016.7793450

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Precision Engineering  

This paper addresses the auto-tuning of a feedforward controller for a linear stage. In our approach, particle swarm optimization (PSO), which is one of meta-heuristic algorithms, is employed. In PSO-based controller tuning, the initial placement and the number of particles are determined a priori. However, the initial placement of particles of the PSO was decided randomly or was not sufficiently discussed. Moreover, although the large number of particles is effective in terms of tuning accuracy, it causes the increase of tuning time. For these reasons, we focus on the setting of the initial placement and the number of particles in order to implement the PSO algorithm appropriate for the controller tuning of the linear stage. To shorten tuning time and improve tuning accuracy, firstly, the initial placement is determined by using the information on the nominal model of the linear stage. Then, since some parameters of the linear stage are known, the dimensionality of particles is reduced. Finally, in consideration of precision positioning, particles are divided into some groups. Furthermore, the number of particles is decided on the basis of the tuning time and the maximum number of iteration. The performance of our initial setting methods is evaluated by simulation and experiment.

DOI： 10.2493/jjspe.82.665

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Inderscience Publishers  

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.

DOI： 10.1504/IJAMECHS.2015.074785

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Five-axes active magnetic bearing (AMB) systems are widely utilized for the field of precision such as semiconductor exposure machines. This paper considers an interpretation of an unbalance vibration compensator PGC for five-axes AMB. As methods for the rejection of periodic disturbance, repetitive control and PIS control, which are based on internal model principle, have been known. The PIS control can be considered as a special case of the repetitive control. This paper investigates the relationship between the PGC and the PIS control from the similarity of the pole assignment and shows that the PGC suppresses the unbalance vibration from the perspective of the internal model principle.

DOI： 10.1109/ICAMechS.2015.7287143

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This paper presents the suppression method of flow disturbance, which is the variation of compressed air supplied to a pneumatic vibration isolator. A central pattern generator (CPG) is utilized to compensate effect of flow disturbance. In order to implement a CPG-based controller, feedback type control scheme, which does not require a pressure sensor, is adopted. Moreover, CPG-based and displacement controllers are connected in parallel so as to avoid the vibration of isolation table during the start-up of isolator. The proposed approach is verified by simulation and experiment.

DOI： 10.1109/ICAMechS.2015.7287150

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper presents the suppression method of anti-resonance and resonance caused by use of air springs, which are the actuator of a pneumatic vibration isolator. Although the relative displacement derivative (RDD) positive feedback control is effective for the suppression of the anti-resonance and resonance, a control system is not causal under the condition that the time delay of response of air springs is present. To overcome this issue, the RDD positive feedback control combined with Smith prediction is used. The effectiveness of the proposed approach is shown by simulation and experiment.

DOI： 10.1109/IECON.2015.7392479

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In semiconductor manufacturing, air type-vibration apparatuses (AVAs) are widely employed. When an earthquake occurs, the AVAs have to be stopped in order to avoid serious damage to semiconductor exposure machines. Spectrum intensity (SI) value is the metric effective for the detection of earthquake though it takes time to calculate this value. To avoid long computation time, this paper uses destructive intensity (DI) value instead of SI value. Simulation demonstrates that DI value, whose computation time is short, can be applied to switching control for AVAs.

DOI： 10.1109/ICAMechS.2015.7287147

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

In this study, we consider the positioning of a pneumatic stage in order to compensate effects of different length of pipes, which connect servo valves and cylinders. Since, in industrial scenes, it is difficult to use pipes of the same length due to the structure of industries, the length of each pipe is often different. In this case, the characteristic of the pneumatic system, which consists of the pipes, servo valves, and chambers, changes in accordance with the pipe length. It leads to two issues: The first one is that the performance of proportional-derivative-double derivative (PDD2) control, which is effective for the control of pneumatic actuators, is degraded. To overcome this issue, the parameter of a pre-compensator for the PDD2 control is tuned. The suitable value of this tuned parameter increases with the length of the pipes. The second one is that the effects of flow disturbance increase due to the different pipe length. When the length of the pipes is not same, it is probable that the magnitude of flow disturbance transmitted to each pipe is different. For this reason, multiple flow disturbance observers (FDOBs) are implemented in a control system. Experimental results show that the repeatability of the positioning is improved by using the FDOBs.

DOI： 10.1299/jamdsm.2015jamdsm0008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

This paper considers the pressure control of air springs used for a pneumatic anti-vibration apparatus (AVA), which isolates vibration transmitted to semiconductor lithography equipment. In the control of the pneumatic AVA, pressure feedback is often employed so as to keep the inner pressure of air springs constant. By expanding the bandwidth of pressure control system, fast response can be obtained, though this bandwidth is restricted due to anti-resonance and resonance in a pneumatic system. To eliminate the anti-resonance and resonance, relative displacement derivative (RDD) positive feedback control has been presented. However, previous RDD positive feedback control cannot be implemented under the condition where the dead time of air springs exists. In order to compensate effects of the dead time, a Smith predictor is utilized. Through experiments, it is shown that in the presence of the dead time, the anti-resonance and resonance can be eliminated by means of the RDD positive feedback control combined with Smith prediction. The bandwidth of the pressure control system increases with the gain of pressure PI compensator. Furthermore, effects of proposed approach on vibration transmissibility are investigated. Although the vibration transmissibility is the performance metric for the development of the pneumatic AVA, the case where the dead time is present was not sufficiently considered. In this paper, it is shown that the vibration transmissibility changes in accordance with the dead time.

DOI： 10.1299/jamdsm.2015jamdsm0031

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Inderscience Publishers  

In the field of precision positioning and measurement, an air-type anti-vibration apparatus is widely used. In order to levitate an isolated table and increase the damping, a position sensor and an acceleration sensor are mounted on the anti-vibration apparatus. The pressure sensor is also utilised for the pressure feedback control, which improves the transmissibility. In the implementation of pressure feedback, the high-resolution pressure sensor is needed. It is, however, expensive. To solve this problem, one approach is to use the observer instead of the pressure sensor. By using the theory of observer, we can choose the pole to determine the convergence of observer. Therefore, in this paper, we investigate effects of parameters of the observer with different pole assignment. The parameters are tuned by considering the frequency characteristics of the anti-vibration apparatus.

DOI： 10.1504/IJAMECHS.2015.070711

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

An air-type anti-vibration apparatus is widely used in the field of precision positioning and measurement. Due to the characteristics of the air spring, a pair of anti-resonance and resonance occurs in the pressure control system. In order to avoid the performance degradation of the vibration control, we eliminate the anti-resonance and resonance by designing the control scheme with an inverse function.

DOI： 10.1109/ICIT.2015.7125092

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper considers the compensation of both flow disturbance and floor vibration for pneumatic anti-vibration apparatuses (AVAs). To compensate for effects of the flow disturbance, repetitive control is employed. When the tunable parameter of a repetitive controller is high gain, the flow disturbance is further suppressed. On the other hand, transmissibility increases. To overcome the trade-off between the flow disturbance suppression and the transmissibility reduction, the setting method of the tunable parameter is presented. In the case of single-loop control system, the transmissibility decreases by using a notch filter as the tunable parameter, whereas in the case of a multi-loop control system, the transmissibility increases at a certain frequency. To avoid this issue, an inverse notch filter is selected as the tunable parameter. It is shown that the transmissibility can be improved by using the inverse notch and notch filters as the tunable parameter.

DOI： 10.1109/ICIT.2015.7125139

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper considers the auto-tuning of a feedforward controller in order to improve the performance of stage positioning. Particle swarm optimization (PSO) technique is employed for the auto-tuning of the controller. In the proposed method, firstly, the dimensionality of the particle in PSO is reduced. Then, the initial placement of each particle is determined by considering the nominal value of the stage. By using these two approaches, the tuning time can be shortened. After the auto-tuning, the settling time of the positioning is improved. Effectiveness of proposed methods is shown by simulation.

DOI： 10.1109/ICIT.2015.7125077

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

For the ultra-precision machining, semiconductor exposure machines employ the pneumatic active anti-vibration apparatuses (AVAs), which have air springs. In industrial scenes, when the vibration due to earthquake is observed, the AVA is automatically stopped by exhausting air. 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 different time delays during shutdown process. To avoid the rotation of the isolated table, reference trajectory is shaped. It is verified that the range of the rotational angle in the shutdown of the AVA can be reduced by using the proposed method.

DOI： 10.1109/ICIT.2015.7125086

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Main movement of a galvano mirror is the rolling motion. However, since the structure of galvano mirror is cantilever, this mirror is vertically vibrated to mirror reflective surface. This paper considers the suppression of the above vibration, which is called pitching vibration. Although the galvano mirror is equipped with an encoder to detect the roll angle of mirror, the pitching vibration of mirror cannot be detected. To overcome this problem, the pitching vibration is verified by the frequency response and the time response using two dimensional position sensitive detector. Moreover, three rubbers with different hardness are inserted on the basis of a structure of the motor shaft in order to suppress the vibration.

DOI： 10.1109/ICAMechS.2015.7287144

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE Computer Society  

This paper considers the model-based controller in order to achieve the high speed and high precision positioning of a linear stage. In the controller design, particle swarm optimization (PSO) is employed for the parameter identification of the linear stage. Particles of the PSO are updated so that the difference between simulation and experimental results becomes small. After the parameter identification, the feedforward controller whose parameters correspond to the identified model of the linear stage is designed. Effectiveness of the proposed method is shown by simulation and experiment.

DOI： 10.1109/ICAMechS.2015.7287145

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper discusses the suppression of temperature change in air springs used for an ant-vibration apparatus. The thermal equivalent circuit, which corresponds to the heat transfer of the air springs, are employed for the evaluation of the temperature change. Based on measurement results of the temperature change and the circuit, four methods are proposed so as to suppress the temperature change. Moreover, previously presented two suppression methods are reexamined from the perspective of the analogy between thermal and electric circuits.

DOI： 10.1109/ICIT.2015.7125150

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper considers the implementation of a proportional-integral-sinusoidal (PIS) control scheme for pneumatic vibration isolators. In this scheme, a sinusoidal compensator (S compensator), which generates a sinusoidal signal, is used to suppress flow disturbance. However, when the S compensator starts up, the vibration of an isolation table occurs. To overcome the issue, a soft switching approach is employed. Moreover, residual high-frequency vibration is attenuated by means of a phase-lead type PIS compensator. The effectiveness of the proposed methods is verified by experiments.

DOI： 10.1109/AIM.2014.6878069

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

An air spring type anti-vibration apparatuses are widely utilized. However, the high resolution sensors are needed for the pressure feedback control. This paper considers pressure estimation of anti-vibration apparatuses. The number of the parameters in the proposed observer is reduced in order to tune parameters efficiently. Moreover, the tuning procedure changes according to the observer poles. The effectiveness of proposed method is shown by experiments.

DOI： 10.1109/ICAMechS.2014.6911569

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In the control of a pneumatic positioning stage, two issues have to be considered. The first issue is the low repeatability caused by variation of parameters in pneumatic system. The second one is the slowness of response due to air compressibility. To overcome these issues, this paper presents the control methods for the pneumatic positioning stage. To compensate for the parameter variation and improve the repeatability, model following control (MFC) is employed. Moreover, to achieve the high-speed positioning, the feedforward (FF) control is utilized. Effectiveness of the MFC and the FF control is shown by experiments.

DOI： 10.1109/ICAMechS.2014.6911570

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Turbo molecular pumps (TMPs), which are equipment to create a vacuum in a closed space, have active magnetic bearings (AMBs). To reduce the size and cost of the TMP, this paper proposes the one-axis AMBs with single side electromagnetic drives. In conventional one-axis AMBs, the electromagnets (EMs) are set over and under the armature disc, whereas the proposed ones utilize the only upper EM. Moreover, permanent magnets (PMs) are attached at the top and bottom side of the rotor to generate magnetic attraction. In this paper, the proposed AMB using single side electromagnetic drive is analyzed and evaluated by simulation and experiments. Furthermore, characteristic variation due to TMP's attitude is considered.

DOI： 10.1109/AIM.2014.6878174

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper presents the effective photography system for the material development of steam turbine blades. By using the proposed system, the image of the turbine blade under high-speed rotation can be visualized. To measure the rotational angle of the blade, a rotary encoder is employed. Since the jitter of electronic circuits increases due to the use of the encoder, a digital pulse generator is included in the photography system. Moreover, a timing controller is used to synchronize the timing of all components in the photography system. Experimental results show that the strain due to the stress applied to the turbine blade is visualized under the condition of high temperature and high speed rotation.

DOI： 10.1109/ICAMechS.2014.6911648

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper deals with the temperature change in the air spring attached to an anti-vibration apparatus. Because in industrial scenes, effects of the temperature of the air spring have not been considered sufficiently, its inner/outer temperature is measured. To suppress the temperature change, the metal absorbing/exhausting the inner heat is used, and the input voltage to servo valve is adjusted. By using both methods simultaneously, the reduction of the temperature change can be further improved. The performance of the methods is evaluated by experiments. Moreover, the thermal equivalent circuit corresponding to the air spring is provided in order to analyze the heat change.

DOI： 10.1109/ICAMechS.2014.6911571

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical Engineers of Japan  

This paper considers the compensation of flow disturbance, which is the variation of air pressure supplied by the air compressor of pneumatic active anti-vibration apparatuses (AVAs). Since the air pressure varies periodically, repetitive control is utilized for the suppression of the vibration induced by the flow disturbance. As the constant gain of the repetitive controller increases, disturbance compensation is improved further. On the other hand, when the gain becomes large, transmissibility increases in the frequency region including the mechanical resonance of AVAs. It leads to the performance degradation of the vibration isolation. In order to overcome the trade-off between the disturbance compensation and the transmissibility, a notch filter is employed instead of the constant gain in the repetitive controller. The center frequency of the filter is set to the frequency region including the mechanical resonance of AVAs so as to avoid the increase of the transmissibility. By using the proposed method, the performance of disturbance compensation can be improved without increasing the transmissibility. Furthermore, effects of parameters for the notch filter are investigated. Experimental and simulation results show that the performance of flow disturbance suppression and the transmissibility of the AVA are almost same regardless of parameters in the notch filter.

DOI： 10.1541/ieejeiss.134.1182

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The pressure of air supplied to pneumatic anti-vibration apparatuses (AVAs) varies periodically. It leads to the vibration of an isolated table. This paper focuses on the suppression of the vibration caused by the pressure variation, which is called flow disturbance. Since the flow disturbance is periodic, repetitive control is employed. The time delay in the repetitive controller is determined by considering the variation of the period of supplied air pressure. When the tunable parameter of the repetitive controller is a large constant gain, the performance of disturbance suppression is improved, whereas the transmissibility increases in high frequency region. To avoid the increase of the transmissibility, a dynamic compensator is selected as the tunable parameter instead of the constant gain. It is shown that a notch filter is the dynamic compensator suitable for the improvement of both the transmissibility and the flow disturbance suppression.

DOI： 10.1109/AIM.2014.6878067

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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.

DOI： 10.1109/AIM.2014.6878070

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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.

DOI： 10.1109/AIM.2014.6878068

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Language：Japanese   Publisher：The Japan Joint Automatic Control Conference  

DOI： 10.11511/jacc.57.0_628

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Language：Japanese   Publisher：The Japan Joint Automatic Control Conference  

DOI： 10.11511/jacc.57.0_97

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

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. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.comnet.2013.07.022

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

This paper considers Smith predictor-based compensation for the dead-time of pneumatic vibration isolators. In the implementation of the predictor, the plant modeling and the dead-time measurement are needed. To improve the model accuracy, the approximation model of pipe resonance is developed. Moreover, to tune parameters of the plant model efficiently, the number of parameters is reduced. The time delay in the Smith predictor is determined by considering the frequency resonance of the control system for vibration isolators. Experimental results demonstrate the effectiveness of our implementation methods. © 2013 IEEE.

DOI： 10.1109/IECON.2013.6699703

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In the field of vibration control of aero space structures, Direct Velocity and Displacement FeedBack (DVDFB) is well-known as an effective control scheme in terms of robustness. However, according to the skyhook control theory, Direct Acceleration, Velocity, and Displacement FeedBack (DAVDFB) is preferable as to manipulate seismic parameters of controlled objects. To contribute for implementation of the DAVDFB, we have proposed a seismic displacement sensor, which can simultaneously detect absolute acceleration, velocity and displacement signals. Prototype sensors have been applied as feedback or feedforward sensors in vibration control of anti-vibration apparatuses. However, due to low detection sensitivity and narrow bandwidth, control performance is not enough for practical use in industrial scenes. Thus, the detection sensitivity is mechanically improved by increasing the number of coil turns, and this effect is evaluated by sensitivity calibration. Moreover, to confirm the effect on practical applications, we carry out control tests of an anti-vibration apparatus with one degree-of-freedom by using the improved displacement sensor.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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 observer's 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.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：E-flow Inderscience  

This paper proposes the control method for vibration caused by variation of air pressure supplied to pneumatic anti-vibration apparatuses. In this method, air pressure variation, i.e., flow disturbance is estimated offline. The time-series data of disturbance estimate is added to the control input signal. Smoothing is utilised to reduce the noise of estimated signal. Moreover, to compensate effects of time-lag of input, two kinds of a shaped signal are also utilised. Experimental results show the effectiveness of the proposed vibration suppression method. Copyright © 2013 Inderscience Enterprises Ltd.

DOI： 10.1504/IJAMECHS.2013.057668

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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.

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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.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

The flow disturbance to a pneumatic vibration isolation table causes periodic fluctuation of the table. In current study, one cycle of flow disturbance is estimated offline using a disturbance observer. The time series data of one cycle estimated disturbance is then stored in the memory of digital signal processor. The program codes are prepared which can detect every cycle of the flow disturbance based on the threshold of table position. The estimated signal is then repeatedly injected from the memory through a compensator to the servo valve to suppress table fluctuation due to periodic actual flow disturbance. The effectiveness of this method is demonstrated by experimental results.

DOI： 10.1299/jamdsm.7.498

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：E-flow Inderscience  

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. Copyright © 2013 Inderscience Enterprises Ltd.

DOI： 10.1504/IJAMECHS.2013.057665

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

Pneumatic active anti-vibration apparatuses (AVAs) are widely employed for the high-precision positioning of wafer stages in semiconductor lithography equipment. However, there exists delay of transmission of air supplied to air springs. In this paper, we consider the suppression of vibration caused by the time delay (i.e., dead-time) of AVAs. The dead-time is compensated by using a Smith predictor, which is well-known as a control method for time delay systems. In the implementation of the predictor, the plant model and the dead-time are needed. For this reason, this paper focuses on the tuning of Smith predictor effective for the control of AVAs. To improve the model accuracy of AVAs, the approximation model of pipe resonance is utilized. Moreover, to determine suitable time delay in the Smith predictor, our methods utilize the resonance frequency of the control system and the tracking error of the isolated table. Conventionally, the nominal value of the dead-time can be obtained by using step response of the control system. On the other hand, it is difficult to exactly estimate the dead-time of AVAs due to position sensor noise. Therefore, the time delay is precisely tuned by proposed methods instead of the step response approach in order to improve the performance of the Smith predictor. Experimental results show that when the error of the time delay in the predictor is zero, the resonance frequency and the time integral become minimized.

DOI： 10.1299/jamdsm.7.666

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In the field of vibration control, accelerometers are widely used as feedback sensors. On the other hand, it is desirable to use a velocity sensor or a displacement sensor without integral operators. Effects of damping and a skyhook spring are obtained by velocity and displacement feedback, respectively. Due to this, an absolute displacement sensor has proposed as a feedback sensor for semiconductor exposure apparatuses. The proposed displacement sensor has the same mechanical structured having a detector and pendulum as a commercial velocity sensor. In authors' previous works, the proposed sensor has been successfully applied as feedback and feedforward sensors. However, detection bandwidth is limited due to mechanical resonances called high frequency dynamics. In this paper, we consider the suppression of high frequency resonance. At first, the modal analysis of the vertical type displacement sensor is conducted in order to investigate vibration modes. Then, the shaking test is also conducted by using the pneumatic active anti-vibration apparatus with the proposed sensor. Finally, we evaluate the performance of the apparatus under the condition that the vertical type displacement sensor is used for feedback control. © 2013 IEEE.

DOI： 10.1109/IECON.2013.6699768

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

This paper proposes a task transmission control with dynamic lightpath setup in an optical grid. In our proposed method, a job manager changes the number of tasks in a resource manager dynamically so as to maintain a constant processing delay. It leads to effective utilization of computing resource. I-PD control is applied to maintain efficient network management. Furthermore, in order to avoid frequent lightpath setup process, multiple lightpaths are established simultaneously by our proposed algorithm. Numerical results show the effectiveness of the proposed task transmission method. (c) 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.21763

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This paper considers a control scheme for the suppression of pneumatic isolation table's fluctuation induced by switching of the feedforward controller. The table acceleration and feedforward paths are added and the combined signal is sent to a damping integrator and gain. The damping integrator, besides generating a damping signal from acceleration signal, also avoids a large jump/drop of the feedforward signal during switching of the feedforward controller. Performance of this control scheme is evaluated by experiments while comparing with conventional control schemes. In addition, retuning of the feedforward compensator's gains is investigated. Based on the experimental results, it is shown that this control scheme can suppress both flow disturbances and switching of the feedforward controller.Copyright © 2012 Inderscience Enterprises Ltd.

DOI： 10.1504/IJAMECHS.2012.045501

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

In this study, a positioning stage is considered, which is actuated by four pneumatic cylinders and vertically supported by four coil-type spring isolators. Previously, we realized the base plate jerk feedback (BPJFB) to be analogues to a Master-Slave system which can synchronize the motion of the stage as a Slave to the motion of the base plate as a Master. However, in the case of real positioning, the stage had slightly self oscillation with higher frequency due to the higher gains set to the outer feedback loop controller besides its oscillation due to the natural vibration of the base plate. The self oscillation of stage was misunderstood to be the natural vibration of base plate due to the reaction force. However, according to the experimental results, the BPJFB scheme was able to control both of the mentioned vibrations. Suppression of the self vibration of stage is an interesting phenomenon, which should be experimentally investigated. Therefore, the current study focuses on the suppression of the self vibration of stage by using the BPJFB scheme. The experimental results show that besides operating as a Master-Slave synchronizing system, the PBJFB scheme is able to increase the damping ratio and stiffness of stage against its self vibration. This newly recognized phenomenon contributes to further increase the proportional gain of the outer feedback loop controller. As a result, the positioning speed and stability can be improved.

DOI： 10.1299/jamdsm.6.252

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Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper considers the automatic parameter tuning for the position control of the linear stage. To improve the performance of the positioning, feedback error learning (FEL), which reduces the output of the feedback controller for the learning, is utilized. Effects of the FEL's parameters (i.e., the reference, the gain of the feedback controller, the learning rate, and the parameter of the feedforward controller) are investigated by experiment. The large amplitude of the reference is effective in terms of the learning accuracy, and the large parameter of the feedforward controller is effective in terms of the learning time. The suitable learning rate and the feedback controller's gain are selected by considering the oscillation of estimated parameters. Furthermore, to shorten the learning time and improve the positioning performance, the termination test of the FEL is presented. In this method, the learning is automatically stopped based on the change of time integral of the estimated vector. Experimental results demonstrate the improvement of the parameter tuning. © 2012 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaic.78.3749

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In this paper, the position control of a linear stage is considered. To improve the settling time of the positioning, the parameters of the feedforward controller are automatically tuned by using feedback error learning (FEL). In the proposed FEL, true value of the estimated parameters is small, and the number of the estimated parameters is reduced. It leads to the improvement of the learning time. Moreover, to compensate for effects of non-parallel guide rails, the disturbance observer is also utilised. By using the observer, the performance of the positioning can be maintained regardless of the initial position of the stage. Experimental results show the effectiveness of our control method. Copyright © 2012 Inderscience Enterprises Ltd.

DOI： 10.1504/IJAMECHS.2012.048399

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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.

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In this paper, we propose a distributed power control algorithm based on PID control and dynamic constraint condition for cognitive radio networks. In our proposed algorithm, at first, each transmitter in secondary networks receives the feedback information about signal-to-interference plus noise ratio (SINR) from its corresponding receiver. Based on the information, the transmitter derives the transmitted power with PID control in order to satisfy the quality of service (QoS) constraints in secondary networks. Then, the transmitter decides the actual transmitted power according to a constraint condition in addition to the derived power. This constraint condition is effective for avoiding the interference with primary networks. Since the constraint condition affects the performance of our proposed method significantly, we propose an effective update algorithm. In the update algorithm, the transmitter changes the constraint condition by comparing the derived transmitted power with both the maximum interference power tolerance and the target SINR. We evaluate the performance of our proposed algorithm with simulation. Numerical examples show that our proposed algorithm is effective for the power control in cognitive radio networks.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In the field of vibration control, accelerometers are widely used as feedback sensors. In addition, according to state feedback control theory, detections of velocity and displacement signals are required to improve anti-vibration performance. Then, an absolute displacement sensor is proposed by modifying a control loop of a seismo-type velocity sensor. Basically, the proposed displacement sensor has the same mechanical structures having a pendulum as a commercial seismo-type velocity sensor. In our previous works, the proposed sensor has been successfully applied as feedback and feedforward sensors. However, it is revealed that bandwidth expansion is necessary as a substitute of the accelerometer. The bandwidth is limited by high frequency resonances observed in high frequency dynamics. In this paper, causes of the resonances are investigated in terms of mechanical resonances of the velocity sensor. At first, operating principles of the velocity and the displacement sensors are explained to show the mechanical structures, and the high frequency dynamics are determined by measuring frequency response functions. Next, experiments on the modal analysis are conducted to specify vibration modes of the pendulum. Finally, the high frequency resonances are suppressed by loading viscoelastic materials.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In the field of vibration control of semiconductor exposure equipments, commercial accelerometers have been used as feed forward 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 feed forward, 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.

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This paper considers high-speed position control of a stage. To improve the performance of positioning, feedback error learning (FEL) control is utilized. In the proposed FEL, free parameters of a feedforward controller are determined such that true value of estimated parameters can become small. Moreover, a priori information on the stage is utilized for learning. Effects of parameters of FEL are investigated in order to improve learning time and accuracy. Experimental results demonstrate that the stage positioning based on the proposed FEL reduces settling time and improves repeatability.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Instrument and Control Engineers  

This paper proposes a method for robust state estimation for systems with irregular sensing failure. It is often experienced that non-contact sensors give abnormal signals (outliers) due to sensing failure. To compensate their effect, the proposed estimator switches observer gains to select normal signals based on the current estimation of the sensor signals. Stability of the error system is guaranteed in terms of switched Lyapunov functions. Both numerical and experimental results show the effectiveness of the proposed method.

DOI： 10.9746/sicetr.47.81

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This paper considers implementation of feedback error learning (FEL) for linear slider position control. The effect of modelling error of the slider is compensated by FEL. In algorithm of FEL, parameters of feedforward controller are updated so that output signals of a feedback controller can become small. It leads to improvement of tracking performance. On the other hand, when conventional FEL algorithm is implemented for control of a linear slider, parameters of the feedforward controller tend to converge slowly. In industrial scenes, it is desirable to shorten learning time in order to reduce cost of setting up manufacturing devices. Furthermore, when the learning time is long, guide rails of the slider become worn. It is shown that convergence speed is improved by tuning free parameters of the feedforward controller. Due to further improvement of the convergence, by using prefilter and free parameters of feedforward controller, some parameters of an inverse system are obtained a priori and utilized for learning. Command with mixed frequency is selected in order to identify accurate inverse system of plant. Simulation results are presented to show the effectiveness of proposed method.

DOI： 10.1299/kikaic.77.3684

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

In this paper a pneumatic positioning stage which is mounted on the base plate and supported by the coil-type spring isolators is considered. The stage is moved by the driving force during positioning and the reaction force causes vibration of the base plate with its natural frequency, which degrades the performance of the positioning. To reduce the effect of the reaction force and improve the positioning time, the base plate jerk feedback is proposed. An external force is used to realize the principle of the base plate jerk feedback based on the theoretical background. The experimental results confirm that the working principle of the base plate jerk feedback obeys the theoretical concepts. The feedback is then employed for the real positioning. Based on the experimental results including repeatability, the effect of the reaction force was considerably reduced and the settling time of the response was improved, after employing the base plate jerk feedback with approximate optimal gain.

DOI： 10.1299/jsdd.5.523

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC MECHANICAL ENGINEERS  

To avoid a longer settling time of an isolation table, switching of the feedforward controller which is used for the control of supplied air's disturbances, is needed after starting and prior to stopping the table. However, this switching also causes the fluctuation of the table. In order to suppress the fluctuation of the table caused by switching, this study uses a difference operator before the feedforward compensator and the combination of feedforward and feedback loops. The effectiveness of this method is experimentally demonstrated.

DOI： 10.1299/jamdsm.5.295

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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This paper considers a networked synchronization of multiple subsystems for cooperative control. When a system sends out local measurement signals to others, transmission delay can take place. We assume that the amount of the transmission delay can be calculated at the receiving instance by using the information of the time-stamp of each packet. Based on this information, the effect of the delay is compensated. Specifically, we design a gain switching observer via LMI (Linear Matrix Inequality) technique for multiple purpose optimization. An experimental result of synchronization of a mini plant with 3 DC-motors is shown to demonstrate its practical effect on the transmission delay. © 2007 IEEE.

DOI： 10.1109/ISIC.2007.4450882

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：THE INSTITUTE OF SYSTEMS, CONTROL AND INFORMATION ENGINEERS (ISCIE)  

This paper considers synchronization of multiple plants over networks. The effect of time-varying transmission delay is compensated by a switching observer which uses the time-stamp information. To calculate the instantaneous value of transmission delay length via the time-stamp, the clocks of sending and receiving computers must be synchronized. It is shown that the correction of the difference of the quartz frequencies of the computers and the clock adjustment via NTP (Network Time Protocol) can provide the time synchronization within a required accuracy for moderate sampling periods. Proposed method is demonstrated by an experiment of synchronization of DC-motors over a real network.

DOI： 10.5687/iscie.21.211

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Instrument and Control Engineers  

Control systems in which signals are transmitted over a network have been attracting great attention recently. In such systems, transmission delay varies irregularly due to congestion of the network. This results in control performance degradation. In order to solve this problem, this paper proposes an observer design method for the systems with time-varying transmission delay. Using a time-stamp of each received packet, the method switches observer gains to estimate the present state of the plant. Then, the observer design is reduced to stabilization of a switched estimation error system. Linear matrix inequalities (LMIs) make it possible to design the observer multiple gains so that the stability of the error system is guaranteed even if the gains are switched randomly. Furthermore, the performance of the gain switching observer is improved by specifying decay rate of a Lyapunov function for the error system. Finally, numerical and experimental examples illustrate the effectiveness of the proposed method.

DOI： 10.9746/sicetr1965.42.1224

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