Oswaldo Horikawa

An attraction-type magnetic bearing with control in a single direction

In past work, the authors have proposed a radial magnetic bearing architecture where the rotor was kept suspended only by means of magnetic forces produced by permanent magnets working in attraction mode and the rotor was actively controlled only in one degree of freedom (d.o.f.), i.e., its axial direction. Although the presented architecture is simpler than those bearings with active control in two or more d.o.f., it presented limitations mainly of low radial stiffness. So, in this context this paper discusses ways to enhance the radial stiffness in this kind of bearing and presents simplified analytical methods used to find magnets and actuator optimal dimensions that gives both ring magnets radial stiffness and actuator force/current ratio maximum intensities.

Design Considerations for Achieving High Radial Stiffness in an Attraction-Type Magnetic Bearing With Control in a Single Direction

In past work, the authors have proposed a radial magnetic bearing architecture where the rotor was kept suspended only by means of magnetic forces produced by permanent magnets working in attraction mode and the rotor was actively controlled only in one degree of freedom (d.o.f.), i.e., its axial direction. Although the presented architecture is simpler than those bearings with active control in two or more d.o.f., it presented limitations mainly of low radial stiffness. So, in this context this paper discusses ways to enhance the radial stiffness in this kind of bearing and presents simplified analytical methods used to find magnets and actuator optimal dimensions that gives both ring magnets radial stiffness and actuator force/current ratio maximum intensities.

Magnetic suspension of the rotor of a ventricular assist device of mixed flow type.

This work presents results of preliminary studies concerning application of magnetic bearing in a ventricular assist device (VAD) being developed by Dante Pazzanese Institute of Cardiology-IDPC (São Paulo, Brazil). The VAD-IDPC has a novel architecture that distinguishes from other known VADs. In this, the rotor has a conical geometry with spiral impellers, showing characteristics that are intermediate between a centrifugal VAD and an axial VAD. The effectiveness of this new type of blood pumping principle was showed by tests and by using it in heart surgery for external blood circulation. However, the developed VAD uses a combination of ball bearings and mechanical seals, limiting the life for some 10 h, making impossible its long-term use or its use as an implantable VAD. As a part of development of an implantable VAD, this work aims at the replacement of ball bearings by a magnetic bearing. The most important magnetic bearing principles are studied and the magnetic bearing developed by Escola Politécnica of São Paulo University (EPUSP-MB) is elected because of its very simple architecture. Besides presenting the principle of the EPUSP-MB, this work presents one possible alternative for applying the EPUSP-MB in the IDPC-VAD.

Robotics applied to work conditions improvement in power distribution lines maintenance

Based on the analysis of the tasks concerning maintenance of power distribution networks from the Ergonomics point of view, Paulista Power & Light Company (CPFL, Brazil) and the University of Sao Paulo (USP, Brazil) started a project focused on the application of Mechatronics and Robotics techniques and knowledge to improve the maintenance activity, also establishing a roadmap of developments to be conducted. As a pioneer research & development on that, four devices are proposed and described herein: (a) A computer-controlled automatic elevator attached to a pickup type lightweight vehicle that helps electricians to reach high positions replacing the conventional ladder; (b) A flexible telescopic robot for inspecting the wood cross arm from the ground; (c) A weight balancer to help electricians to execute tree trimming around distribution lines, by reducing the physical effort required for holding and manipulating the trimming equipment; (d) And a mechatronics version of the weight balancer able to automatically adapt to different loads.

Experimental development of a one-degree-of-freedom controlled magnetic linear bearing

We describe the architecture of a magnetic linear bearing with active control in only one direction, namely, the transverse direction of a moving table. The motions in the remaining directions, except the transverse direction, are restricted only by the action of permanent magnets. A control system composed of two electromagnets, a gap sensor, and a controller, keeps the table in a fixed transverse position. We explain the principle, the dynamic model for controlled direction, and the control system for the bearing. Finally, we describe experiments conducted on a prototype that show the effectiveness of the bearing architecture.

Automatic elevator system for maintenance services

This work presents an electrically assisted automatic elevator system for maintenance of street lights. The system was installed in a public illumination maintenance truck. It consists of a telescopic column, a base structure, and a platform. The whole operation is monitored and controlled by a PLC. The system aims at reducing efforts in maintenance tasks as well as improving the work conditions for the electricians.

Single Axis Controlled Hybrid Magnetic Bearing for Left Ventricular Assist Device: Hybrid Core and Closed Magnetic Circuit

In previous studies, we presented main strategies for suspending the rotor of a mixed-flow type (centrifugal and axial) ventricular assist device (VAD), originally presented by the Institute Dante Pazzanese of Cardiology (IDPC), Brazil. Magnetic suspension is achieved by the use of a magnetic bearing architecture in which the active control is executed in only one degree of freedom, in the axial direction of the rotor. Remaining degrees of freedom, excepting the rotation, are restricted only by the attraction force between pairs of permanent magnets. This study is part of a joint project in development by IDPC and Escola Politecnica of São Paulo University, Brazil. This article shows advances in that project, presenting two promising solutions for magnetic bearings. One solution uses hybrid cores as electromagnetic actuators, that is, cores that combine iron and permanent magnets. The other solution uses actuators, also of hybrid type, but with the magnetic circuit closed by an iron core. After preliminary analysis, a pump prototype has been developed for each solution and has been tested. For each prototype, a brushless DC motor has been developed as the rotor driver. Each solution was evaluated by in vitro experiments and guidelines are extracted for future improvements. Tests have shown good results and demonstrated that one solution is not isolated from the other. One complements the other for the development of a single-axis-controlled, hybrid-type magnetic bearing for a mixed-flow type VAD.

On the influence of thermal hysteresis on the performance of thermomagnetic motors

Although thermal hysteresis might be a problem in the magnetocaloric refrigeration, the same is not necessarily true for thermomagnetic motor applications. This work presents a comparison of the magnetocaloric properties of materials with first order magnetic transition (having large or narrow thermal hysteresis) to those with second order magnetic transition, assessing the application of these materials in thermomagnetic motors through a thermodynamic approach. Results show that the larger the thermal hysteresis, the higher the specific work produced in a thermal cycle. This allows operation at higher temperature differences with high efficiency relative to Carnot efficiency, when compared with systems using narrow hysteresis and second order transition materials.Although thermal hysteresis might be a problem in the magnetocaloric refrigeration, the same is not necessarily true for thermomagnetic motor applications. This work presents a comparison of the magnetocaloric properties of materials with first order magnetic transition (having large or narrow thermal hysteresis) to those with second order magnetic transition, assessing the application of these materials in thermomagnetic motors through a thermodynamic approach. Results show that the larger the thermal hysteresis, the higher the specific work produced in a thermal cycle. This allows operation at higher temperature differences with high efficiency relative to Carnot efficiency, when compared with systems using narrow hysteresis and second order transition materials.

Analytic and Experimental Analysis of Magnetic Force Equations

The design of magnetic devices requires a precise estimation of magnetic forces. In previous works, we presented a general approach to estimate these forces based upon thermodynamically closed systems, resulting in four different forms of the force equations. This paper presents a complete theoretical model analysis tested by experiments, using arrangements of permanent magnets and a device for measuring the force induced on a soft magnetic material according to its position with respect to the permanent magnets. The results of analytical formulation, Finite Element Method numerical analysis, and experiments are compared with each other. This enabled the identification of two forms of the force equations that most precisely describe the magnetic forces. A follow-up experiment is then proposed and executed, identifying the correct form of the magnetic force equations. The resulting equation can be used to analytically estimate the magnetic force in many practical problems.

Double conical wheels based mobile robot for aerial power distribution lines inspection

There are several proposals of robots for inspection of overhead power network, and most of them make use of UAVs (Unmanned Aerial Vehicle). Such proposals present disadvantages like, low controllability, small payload capability and short operation range. On this scenario, this work presents a robot that can move over the power line and has as features: three driven wheels, distributed control system and self-configuration frame. The robot can overpass all power line devices taking the advantage of its wheels shape that provides a self-steering capability. The communications between each motor controller is done by IEEE 802.15.4 wireless communication standard. The robot can be controlled by an electrician to proceeds the inspection from the ground level or in an autonomous way. A prototype was constructed and was tested, in both, laboratory and field environment. The test results shown the effectiveness of the robot proposed.