As the rotational speed of conventional rotor systems supported by oil-film bearings has increased, vibration problems such as oil whip and oil whirl have become apparent. Our group proposed the use of active magnetic bearings (AMBs)/bearingless motors (BELMs) to stabilize these systems. In such a system, measuring the variable stiffness and damping of the oil-film bearings, the current-force and displacement-force parameters of the AMBs/BELMs, and the residual unbalanced force is necessary to satisfy the stability of the rotor system. These parameters are the foundation for the rotor dynamics analysis and optimization of the control strategy. In this paper, we propose a method to simultaneously identify the parameters of the oil-film bearings and AMBs/BELMs along with the residual unbalanced forces during the unbalanced vibration of the rotor. The proposed method requires independent rotor responses and control currents to form a regression equation to estimate all the unknown parameters. Independent rotor responses are realized by changing the PID control parameters of the AMBs/BELMs. Numerical simulation results show that the proposed method is highly accurate and has good robustness to measurement noise. The experimental results show that the unknown parameters identified by the responses generated by different controller parameters are similar. To confirm that the identification results are correct, verification experiments were carried out. The vibration amplitude of the rotor was successfully suppressed by applying a force to the rotor in the opposite direction to the residual unbalanced force. The frequency response characteristics and unbalanced responses of the rotor estimated by the values of the parameters identified show good consistency with the measured results.

The high biocompatibility and high durability of disposable extracorporeal centrifugal blood pumps (CBPs) utilizing magnetic bearing or bearingless motor technology make them perfect for supporting cardiopulmonary circulation for patients. However, the rotor incorporated in the disposable unit typically uses high-cost and environmentally-unfriendly rare-earth permanent magnets (PMs), leading to economic and environmental issues. This paper proposes a centrifugal blood pump with a PM-free impeller/rotor in the disposable pump head utilizing a 12/8 bearingless switched reluctance slice motor (BELSRM). Two axial-magnetized PM rings and two iron rings are mounted symmetrically above and below the tips of the stator poles. The biased magnetic flux generated by the PM rings forms a closed vertical magnetic circuit (homopolar flux circuit) with a PM-free rotor, providing high passive stiffness and large positioning forces independent of the rotor angle. A three-dimensional (3D) finite element analysis (FEA) model was used to evaluate the rotor support stiffness, the current-force coefficient, and the rotational torque. A prototype bearingless slice motor (BELSM) and a disposable pump head with a diameter of 50 mm PM-free impeller/rotor were fabricated. The radial magnetic levitation and the rotation were actively controlled by displacement and speed feedback control systems, respectively. A mock circulatory loop filled with 40wt% aqueous glycerol solution was set to evaluate the performance of the proposed CBP. The CBP provided a maximum flow rate of 4.59 L/min and a maximum head pressure of 214.5 mmHg at 2300 rpm and 2400 rpm, respectively.

Bearingless slice motors (BELSM) employing active radial positioning control and passive stabilization in the axial and tilt directions are widely utilized in medical and industrial applications. Conventionally, the radial displacement of a BELSM is measured by arranging eddy current displacement (ECD) sensors either outside or inside the rotor to detect its radial movement. However, this sensor placement method either increases the rotor’s height because of an additional sensor target or occupies the inner space because of the sensor holder. To address this issue, we propose the mounting of ECD sensors on the underside of the inner edge of the rotor for radial displacement measurements. However, formulating the radial displacement from the sensor outputs is challenging because of complex sensor nonlinearities and the effects of axial movement and tilt. To resolve this problem, we propose the usage of seven ECD sensor placements and establish relationships between the sensor outputs and radial displacement. Initially, displacement estimation based on the polynomial fitting method is proposed, however, it results in unacceptable measurement errors owing to sensor calibration errors. Subsequently, a neural network (NN) method is proposed, which exhibits good linearity within ±150 μm and a measurement bandwidth of up to 200 Hz. The NN is further implemented into the displacement feedback system, enabling magnetic suspension startup and rotation with a radial displacement measurement error controlled within 16 μm within 1700 rpm. Diverse and large datasets, coupled with an increased number of sensors can substantially enhance measurement accuracy.

We present a novel heteropolar bearingless slice motor (BELSM) with a PM-free rotor for a disposable centrifugal blood pump. The new motor adopts a triple-layer biased heteropolar magnetic field in the air gap, including two-layer sliced magnetic coupling generated by multipole ring magnets and a one-layer motor field. The biased motor field is induced by the PM sandwiched between the stator teeth and yoke for generating torque and the suspension force. Due to the unique triple-layer biased field, the motor possesses high passive stiffness in the axial and tilt directions. Additionally, a high torque density is achieved due to the biased heteropolar field induced by the permanent magnet, which allows bipolar current injection. As a result, the motor can transmit a greater amount of electromagnetic energy through the air gap. Thus, the motor achieves both a high torque density and high passive stiffness. Furthermore, the presence of a stationary biased flux enables the regulation of the suspension force generation to be independent of the rotor angle. This decoupling of the rotational and suspension control enables separate and simplified control strategies for the motor operation. FEA simulations were conducted to estimate the torque density and the passive stiffness of the BELSM. The results of the simulation were validated by tests on a prototype.

Purpose: This paper proposes a flexural ultrasonic transducer specifically designed for surface treatment of materials with delicate surfaces such as skin by acoustic cavitation at low frequencies. The goal of this preliminary study is to assess the resonance frequencies and the output sound pressure of the proposed transducer and confirm generation of acoustic cavitation on the surface of an artificial skin phantom. Methods: A transducer prototype was designed based on structural-acoustic simulation and fabricated. The proposed design employs a concave-shaped acoustic resonator with a spherical cavity, which is driven by flexural vibration of a piezoelectric ceramic disk actuator. The transducer prototype has compact dimensions of 15 mm in diameter and 8 mm in axial length, working at frequencies around flexural vibration modes of the piezoelectric disk with a thickness of 1 mm. Results: The maximum sound pressure amplitude reached 125 kPa with an input voltage amplitude of 10 V at the second resonance frequency of 167 kHz, where the third axisymmetric eigenmode was excited. Despite enhancing the maximum pressure, the sound pressure outside the resonator attenuates because the near-field distance of the irradiated sound wave is smaller than the height of the resonator. This implies that the proposed method provides the cavitation effect on material surfaces, possibly minimizing the side effect of ultrasound irradiation on the underlying structure. Cavitation generation on a urethane gel surface was directly observed by using a high-speed video camera. Conclusion: We confirmed that acoustic cavitation was generated and propelled to the target surface. It concludes that ultrasound irradiation using the proposed ultrasonic transducer could be a promising alternative for effective and safe ultrasound treatment of material surfaces.