Takeshi Mizuno

Bio: Takeshi Mizuno is an academic researcher from Saitama University. The author has contributed to research in topics: Electromagnetic suspension & Magnetic bearing. The author has an hindex of 18, co-authored 305 publications receiving 1690 citations.

Vibration Isolation System Using Negative Stiffness

Abstract: A new vibration isolation system using negative stiffness realized by active control technique is proposed in this paper. The serial connection of a normal spring and a suspension system with negative stiffness enables the isolation system to have low stiffness for vibration from the ground and high (theoretically infinite) stiffness against direct disturbance acting on the isolation table. A control method of realizing negative stiffness with a linear actuator is presented in an analytical form. The validity of this method is confirmed experimentally with an apparatus equipped with a voice coil motor. It is also confirmed experimentally that high stiffness against direct disturbance on the isolation table can be achieved in the proposed vibration isolation system.

Application of digital signal processors for industrial magnetic bearings

Abstract: Active magnetic bearings (AMBs) are an example for industrial applications of digital signal processors (DSPs). The complex control functions involved include multichannel control in a delay-time sensitive system. DSPs are well suited for this challenging application. Hardware and software issues are discussed. Unbalance compensation and other additional functions of the controller are presented. An industrial milling spindle with AMBs and DSP control is discussed in detail. A section on AMB research projects with DSP control indicates future trends. >

Development of a three-axis active vibration isolator using zero-power control

Abstract: This paper presents the development of an active 3-degree-of-freedom (DoF) vibration isolation system using zero-power magnetic suspension. The developed system is capable to suppress direct disturbances and isolate ground vibrations of the 3-DoF motions, associated with vertical translational and rotational modes. Two categories of control strategy for the actuators are proposed, i.e., local control and mode control. The latter method allows to overcome limitations of the poor performances for rotational modes exhibited by the former. A mathematical model of the system is derived and each DoF motion is treated separately for the control system. It is demonstrated analytically that the infinite stiffness to static direct disturbances can be generated and the resonance peak due to floor vibration can effectively be suppressed for the system. Moreover, the experiments have been carried out to measure the static and dynamic responses of the isolation table to direct disturbances, and transmissibility characteristic of the isolator from the floor. The results indicate good vibration isolation and attenuation performances, and show the efficacy of the developed isolator for industrialization

Stability analysis of self-sensing magnetic bearing controllers

Abstract: The controllers designed for position-sensorless voltage-controlled active magnetic bearings (AMBs) are investigated from the viewpoint of strong stabilization. First, magnetic bearings with laminated iron cores are treated in which the effects of eddy currents are negligible. It is shown that full- and reduced-order observer-based stabilizing controllers differ in stability; any reduced-order observer-based stabilizing controller is always unstable while most of the full-order observer-based stabilizing controllers are stable. Second, self-sensing suspension in magnetic bearings with solid iron cores is discussed. It is shown that the full-order observer-based stabilizing controller is destabilized by a modification including the effects of eddy currents flowing through the cores. It accounts for the difficulty of actual self-sensing suspension in solid-cored magnetic bearings.

Haptic device with indirect haptic feedback

Abstract: A haptic device provides indirect haptic feedback and virtual texture sensations to a user by modulation of friction of a touch surface of the device in response to one or more sensed parameters and/or time. The sensed parameters can include, but are not limited to, sensed position of the user's finger, derivatives of sensed finger position such as velocity and/or acceleration, sensed finger pressure, and/or sensed direction of motion of the finger. The touch surface is adapted to be touched by a user's bare finger, thumb or other appendage and/or by an instrument such as a stylus held by the user.

Adaptive Backstepping Control for Active Suspension Systems With Hard Constraints

Abstract: This paper proposes an adaptive backstepping control strategy for vehicle active suspensions with hard constraints. An adaptive backstepping controller is designed to stabilize the attitude of vehicle and meanwhile improve ride comfort in the presence of parameter uncertainties, where suspension spaces, dynamic tire loads, and actuator saturations are considered as time-domain constraints. In addition to spring nonlinearity, the piecewise linear behavior of the damper, which has different damping rates for compression and extension movements, is taken into consideration to form the basis of accurate control. Furthermore, a reference trajectory is planned to keep the vertical and pitch motions of car body to stabilize in predetermined time, which helps adjust accelerations accordingly to high or low levels for improving ride comfort. Finally, a design example is shown to illustrate the effectiveness of the proposed control law.

Unbalance compensation using generalized notch filters in the multivariable feedback of magnetic bearings

Abstract: Unbalance of magnetically levitated rotors causes undesirable synchronous vibrations which may lead to saturation of the magnetic actuator. To avoid this problem we propose a generalized narrow-band notch filter which is inserted into the multivariable feedback without destabilizing the closed loop. The parameters of the generalized notch filter strongly depend on the inverse sensitivity matrix evaluated at rotational speed. This matrix is easily measured a priori and stored in a look-up table. It is shown that a decentralized notch is feasible for weakly gyroscopic rotors. The proposed notch filter approach has advantages in terms of run-time complexity and analytical verification of closed-loop stability. Results from the implementation of the proposed unbalance compensation in industrial magnetic bearing systems are included.