Yohji Okada

Analysis and comparison of PM synchronous motor and induction motor type magnetic bearings

In this paper, a general solution of radial position control applicable to PM synchronous type and induction type rotating motors is presented. The rotor of the permanent magnet motor is assumed to have sinusoidally distributed magnetic poles along the axial surface, while the rotor of the induction type motor is assumed to have uniform magnetic property. The inner wall of the stator is also assumed to have a current sheet, which can produce an arbitrary current distribution. The same number of magnetic poles gives the rotating torque to the rotor, while plus/minus two poles of the motoring control produces a pure radial force to the rotor. By controlling the magnitude and phase of the plus/minus two-pole current distribution relative to the motoring magnetic pole, the radial force can be controlled in the radial coordinate. This general solution is experimentally confirmed by using a simple experimental setup. >

Mixed flow artificial heart pump with axial self-bearing motor

With the objective of developing a small blood pump with a levitated rotor, we propose a design scheme for an axial-type self-bearing motor. The axial type motor, which is basically composed of a disc motor and an axial magnetic bearing, controls both the rotation and the axial translation of the rotor. The proposed motor is similar to the bidirectional disc motor, except for changing the magnitudes of both sides of the flux to control the axial attractive force. However, the radial and tilt directions rely on passive stability, and, therefore, the rotor has poor damping which might cause damage to blood constituents. The design includes a hydrodynamic bearing for improving radial support properties. Finally, to confirm its functionality, an experimental prototype of the proposed motor has been constructed and incorporated into a mixed flow blood pump. The results indicated that the bidirectional axial-type self-bearing motor had high efficiency as a small continuous flow blood pump, delivering sufficient flow rate and pressure head.

Characteristics and control of a bidirectional axial gap combined motor-bearing

Introduces the design characteristics of a bidirectional axial gap combined motor-bearing where the flat disc motor has both rotation and axial position control capability. This motor consists of a disc rotor with a stator on each side of the rotor. The axial motion of the rotor is actively controlled while the other axes are constrained by additional passive or active radial magnetic bearings. Each stator produces a rotating magnetic flux in the air gap, to generate the motor torque. The axial force is controlled by changing the amplitude of the rotating flux. Both permanent-magnet motor and induction motor versions were analyzed theoretically and tested experimentally. The results demonstrated the capability of providing both the functions of a motor and a magnetic bearing.

Variable Resistance Type Energy Regenerative Damper Using Pulse Width Modulated Step-up Chopper

This paper describes a new technique for improving the damping property and efficiency of an energy regenerative damper It is intended for a linear DC motor type vibration damper to regenerate vibration energy efficiently. Normally a regenerative damper can regenerate vibration energy only at high speed motion. For low speed motion, the damper has nonlinear characteristics with dead zone and cannot regenerate energy. In order to overcome this problem, a step-up chopper is introduced between the actuator and the charging circuit. The energy is regenerated from low speed and low voltage actuator to high voltage charging circuit. This paper also proposes a new control technique to the step-up chopper by using pulse width modulated signals. The damper can change its damping coefficient and the energy can be regenerated more efficiently. The proposed damper is applied to an active mass damper system. A simple experimental setup is used to validate the proposed technique. The results show an increase in performance and energy regeneration as compared to the previously proposed regenerative damper.

Regenerative control of active vibration damper and suspension systems

A new energy regenerative type vibration damper and suspension systems are introduced. It is intended for active damper to reduce energy consumption without losing damping efficiency. An electro-dynamic actuator is used for the regenerative damper. The electric energy is regenerated during the high-speed motion of the actuator. For low-speed motion, an active or passive control algorithm is applied to the same actuator to achieve a good damping performance. This idea is applied to a single degree-of-freedom vibrating system. The experimental results show that the system has better performance than the pure passive damper system and can regenerate vibration energy.

Self-sensing Active Vibration Control using the Moving-Coil-Type Actuator

Active vibration control requires a velocity signal which is fed back to the force actuator to produce the damping force to the structure. Usually a gap sensor is used to detect the displacement and a differentiator is needed to produce the velocity signal. Moreover, it is very difficult to install the sensor at the same position of the actuator. Setting the gap sensor close to the magnetic actuator may cause an undesirable interaction between them. Sometimes there is no space for installing the sensor. This paper introduces a method of using a moving-coil-type actuator as a two-port sensing and driving device. Four types of velocity identification algorithms are tested and their capability of reducing structural vibrations is compared.

New design of hybrid-type self-bearing motor for small, high-speed spindle

A new structure of hybrid (HB)-type self-bearing motor is proposed for miniature spindle motors. The proposed design combines the HB-type self-bearing motor and HB active magnetic bearing in the common stator and rotor pair to generate large radial forces. First, the principle and theoretical background are introduced. Then, the air gap flux is analyzed by the finite element method, and radial forces for the proposed and standard-type HB self-bearing motors are compared. Finally, experiments are conducted to confirm the performance of the proposed motor. The motor can run at relatively high rotating speed with relatively high torque compared with its small size. The levitation is very stable and the motor indicates good performance for practical application.

Magnetically suspended centrifugal blood pump with a self bearing motor.

A magnetically suspended centrifugal blood pump with a self bearing motor has been developed for long-term ventricular assistance. A rotor of the self bearing motor is actively suspended and rotated by an electromagnetic field without mechanical bearings. Radial position of the rotor is controlled actively, and axial position of the rotor is passively stable within the thin rotor structure. An open impeller and a semi-opened impeller were examined to determine the best impeller structure. The outer diameter and height of the impeller are 63 and 34 mm, respectively. Both the impellers indicated similar pump performance. Single volute and double volute structures were also tested to confirm the performance of the double volute. Power consumption for levitation and radial displacement of the impeller with a rotational speed of 1,500 rpm were 0.7 W and 0.04 mm in the double volute, while those in the single volute were 1.3 W and 0.07 mm, respectively. The stator of the self bearing motor was redesigned to avoid magnetic saturation and improve motor performance. Maximum flow rate and pressure head were 9 L/min and 250 mm Hg, respectively. The developed magnetically suspended centrifugal blood pump is a candidate for an implantable left ventricular assist device.

Design and control of a disk-type integrated motor-bearing system

A disk-type integrated motor-bearing system having axial magnetic flux is newly invented and its design, analysis, and control methods are presented. Sinusoidal motoring currents to four symmetrically placed winding groups produce a torque, whereas control currents of the same magnitude but opposite signs added to the opposite winding groups create radial forces. The control currents are intended to break force symmetry, resulting in unbalanced radial forces. The system employs two stators not only to effectively remove the rotational frequency modulation effect in the radial control forces, but also to reduce the torque ripple. It is shown that the prototype integrated motor-bearing system built in the laboratory succeeds in stable radial direction control and operation of the rotor.

Self-Sensing Active Suppression of Vibration of Flexible Steel Sheet

In rolling processes, flexible steel sheet is supported by rollers and is bound to produce structural vibration. This vibration can cause severe problems to surface finish and affect the quality of the product. To overcome these problems, active vibration control has been proposed. This usually requires both sensors and actuators. The location of sensors and actuators plays a very important role in active vibration control. Moreover, a reliable sensor can be very expensive. This paper proposes a self-sensing vibration control using a push-pull type electromagnet to control the transverse vibration of the steel plate. The construction of the electromagnet has two types of coils, namely the bias coil and the control coil. Vibration displacement is estimated by using the mutual inductance change between the bias and the control coils. The estimated signal is proportional to the gap displacement. The proportional and derivative signals are fed back to the control coil to reduce the transverse vibration of the steel sheet. The proposed method is applied to a simple test rig to confirm the capability of the device. The results obtained are showing high possibility for reducing steel sheet vibration.