A self-bearing motor (SBM) is an electric motor with a magnetically integrated bearing function, that is, it can provide levitation and rotation simultaneously as a single actuator. This paper presents the design, operating principle and control system for the slotless self-bearing motor (SSBM). In this design, the stator has no iron core but includes six-phase coils. The rotor consists of a permanent magnet and an enclosed iron yoke. Magnetic forces generated by the interaction between stator currents and the magnetic field of the permanent magnet are used to control the rotational speed and radial position of the rotor. In this paper, the torque and radial bearing forces are analyzed theoretically with the aim to develop an improved control system. In order to confirm the proposed control method, an experimental system was constructed and tested. Simulation and measurement results show that the SSBM can work stably in modes such as start, reverse, rotation load and external radial pulse forces.
The authors acknowledge and thank the Ministry of Science and Technology of the Republic of China for their partial financial support of this study under Contract Number MOST 109-2622-E-992-008 -CC3.
Nowadays, small- and medium-sized enterprises play crucial roles in both developed and developing countries. They create new employment, fulfill the market gap, contribute to Gross Domestic Product and boost the whole economy. However, small- and medium-sized enterprises face more financial constraints than large enterprises, which prevent them from growing and expanding their activities. This paper aims to investigate how the innovation of small- and medium-sized enterprises impacts on credit accessibility in Vietnam from 2005 to 2015, through five aspects of innovation: new products, new technology, improved existing products, research and development investment, and machine innovation. The data set consists of more than 4500 observations of small- and medium-sized enterprises in Vietnam. This data set is taken from a survey conducted within the framework of cooperation among UNU-WIDER, the University of Copenhagen and Vietnamese government agencies. Using panel regression model, we found out that three out of five innovation factors significantly impact on credit accessibility. More specifically, research and development investment and new product have negative impact on credit accessibility; whereas new technology has positive impact on credit accessibility. These findings are useful for firm managers, banks and policy makers to help small- and medium-sized enterprises overcome financial constraints through innovation aspects.
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