Satoru Fukata

Superconducting bearing systems using high Tc superconductors

To realize the practical use of superconducting bearings, three types of superconducting bearing systems using high Tc superconductors are constructed. This paper describes static characteristics such as load capacities of the bearings and dynamic characteristics of the rotors. Spin-down tests of the rotors are performed to evaluate dynamics of the systems. One of three rotors of the bearing systems is very well self-centered in the speed range not exceeding 63000 RPM. The displacements of the rotor are smaller than 30 /spl mu/mp-p (peak to peak) except near the critical speeds.<<ETX>>

On the determination of the optimal feedback gains for multivariable linear systems incorporating integral action

In this paper we present a technique of obtaining the optimal feedback gains for multivariabe linear systems incorporating integral action. Unlike the methods proposed up to now, a performance index in this paper is the practical quadratic one which does not penalize either the integration of output error or the time derivative of control, therefore giving a reasonable solution. The necessary condition for the solution is given by the non-linear simultaneous matrix equations which can be solved by a gradient technique. Also we suggest a minimax solution which minimizes the worst case in order to get practical feedback gains.

Vibration suppression of a disk-shaped superconductor with PD control

Abstract In order to investigate superconducting magnetic bearings (SMBs) using repulsion forces between superconductors and electromagnets, an experimental setup for a thrust SMB able to move in one direction has been made. The experimental setup is composed of a high T c superconductor, permanent magnets, electromagnets and a Hall sensor. The superconductor used in this paper is supported by the permanent magnets in the radial direction. The vibration of the superconductor is suppressed by an analog PD (proportional and derivative) controller. From the experiments, it is found that suppressing the vibration is well performed by the PD controller. Also, it is found that the controller needs more resistance against disturbance caused by the pinning effect.

Evaluations of a hybrid-type superconducting magnetic bearing system

This paper describes a hybrid-type superconducting magnetic bearing (SMB) system. The system is composed of a pair of SMBs and a pair of active magnetic bearings (AMBs). The hybrid-type SMB system does not need bias currents applied to the electromagnets for supporting the rotor, because the rotor mass is supported by the SMBs. The displacements of the rotor are suppressed by both the SMBs and the AMBs. The superconductors of the SMBs were field-cooled. Comparison of the impulse response of the rotor in the hybrid-type SMB system and that with only SMBs working highlights the good performance of the former. In order to investigate the usefulness of the hybrid-type SMB system, displacements of the rotating rotor and energy loss of the system are discussed.

Determination of the feedback gains of sampled-data linear systems with integral control using time-weighted quadratic performance indices

Sampled-data feedback control with integral action, minimizing time-weighted quadratic performance indices, is considered for continuous linear systems, The necessary conditions to be satisfied by the feedback gains are developed by using the parameter optimization technique. To remove the dependence of the solution on reference inputs and external disturbances, the performance index based on statistical expectation is considered. The necessary conditions are solved by a gradient technique. Numerical examples are given to illustrate the effect of a time-weighted performance index on the transient responses of the output.

Optimization of linear systems with integral control for time-weighted quadratic performance indices

The necessary conditions to be satisfied by the feedback control constructed by available variables, minimizing time-weighted quadratic performance indices for linear systems incorporating integral action, are developed using the parameter optimization technique. To remove the dependence of the solution on a reference input and an external disturbance, a performance index based on the statistical expectation and a minimax solution are considered. An algorithm based on a gradient technique is given to solve the necessary conditions of the minimax solution. Numerical examples are given to illustrate the effect of a time-weighted performance index on the transient response of the output, and they show that the integral-square-time-square error performance index is acceptable for a reference input.

On sampling period sensitivities of the optimal stationary sampled-data linear regulator

In this paper the stationary sampled-data linear regulator is considered. The third and fourth-order sensitivities, about the zero sampling period, of the cost matrix and the third-order sensitivity of the feedback gain matrix are computed. Also the first and second-order sensitivities, about an arbitrary sampling period, of the cost and feedback gain matrices are computed. Moreover, the relationships between the cost matrix sensitivities and the feedback gain matrix sensitivities are made clear.

Development of a hybrid-type superconducting magnetic bearing system

Abstract To further the practical use of superconducting magnetic bearings (SMBs), a hybrid-type SMB system consisting of SMBs, active magnetic bearings (AMBs) has been developed. The hybrid-type SMB system does not need bias currents applied to the electromagnets for supporting the rotor because the rotor mass is supported by the SMBs. The displacements of the rotor position are suppressed by both the SMBs and the AMBs. The superconductors of the SMBs were field-cooled. Impulse responses of the rotor in the hybrid-type SMB system, the system with only SMBs working, and the system with only AMBs working are investigated. The results show that the hybrid-type SMB system has a good performance in impulse responses. Dynamic modeling of the bearing system is also discussed.

The evaluation of time-weighted quadratic performance indices for discrete and sampled-data linear systems

Time-weighted quadratic performance indices are evaluated for discrete and sampled-data linear systems. An evaluation in simple form is presented for discrete systems using a direct method based on manipulating the matrix infinite series. The result obtained is applied to sampled-data systems in which the performance index is given by the integral of continuous-data errors. It is shown that the result for sampled-data systems leads to the result for continuous systems when the sampling period approaches zero.

A New type of superconducting bearing system using high Tc superconductors and the dynamics

Abstract To further the practical use of superconducting bearings, a superconducting bearing spstem using high Tc superconductors has been neplp constructed. The superconducting bearing spstem consists of tpo superconducting bearings and a rotor. The rotor is supported bp the bearings pith field-cooled superconductors. Static and dpnamic characteristics of the superconducting bearing spstem are investigated. To evaluate the load capacitp of the spstem, relationships betpeen restoring force and displacements of the rotor in the radial direction and the axial direction are investigated. Moreover, to construct a vibration model of the superconducting bearing spstem, responses for impulsive forces applied in the radial direction of the stationarp rotor are measured using an FFT analpper. The rotor has a maximum speed of 63,000 rpm driven bp air force. Spin-dopn tests are performed to evaluate dpnamics of the rotor, after the driving force is cut off. The results shop that the displacements are smaller than 30 μm peak to peak at all speeds except critical speeds of the spstem. The bearing spstem is verp pell self-centered in the speed range up to 63,000 rpm in our experiments. Since the structure of the superconducting bearing spstem is verp simple and easp to use, the bearing spstem is full of promise for industrial applications.