Smaller and lighter motors are needed to be used for cooperative robots, which are becoming a recent issue among articulated robots. In order to make the motor small, the axial length must be reduced within a limited diameter, so a reduction in the length of the core lamination and the winding end length must be considered. However, loss and thermal analysis are essential in the design process, as loss increases to meet output with excessive volume reduction and may consequently increase temperature severely. In this paper, the magnetic performance for various analytical models studied to reduce the axial length is invested, and the thermal behavior is predicted by the analytical lumped-circuit method. A model with the trade-off between the low temperature-rise and high magnetic performance among several analytical models is selected. The magnetic characteristics and predicted temperature-rise are compared to the measured results and found to be quite consistent.

This paper presents the design of an axial-flux permanent-magnet (AFPM) generator used for hybrid electric propulsion drone applications. The design objectives of the AFPM generator are high power density, which is defined as output power per generator weight, and high efficiency. In order to satisfy the requirements for the target application and consider the practical problems in the manufacturing process, the structure of the AFPM generator comprising a double-rotor single-stator (DR-SS) was studied. In order to determine the rotor topology and stator winding specifications that had the greatest impact on performance in the DR-SS type design process, we selected three rotor models according to the arrangement of the magnetization direction and three stator models according to the coreless winding specifications. These models were first compared and analyzed. Then, a 3-D finite element method was performed to calculate the magnetic, mechanical, and thermal characteristics of the designed models. By consideration of the output power, efficiency, temperature, and mechanical stability, etc., a topology suitable for the design of generators for UAV systems was determined and manufactured. The reliability of the design result was confirmed through the test.

In this paper, we propose a method to efficiently design joint motors, which are the key elements that drive a cooperative robot. Designing joint motors with more power than the required capacity increases the volume and weight of the robot. On the other hand, designing joint motors with less power than the required capacity can lead to failure and safety accidents because of high temperature rise and mechanical instability. Therefore, in this study, the required capacities of the joint motors were determined through a dynamic analysis of the robot system and incorporated in the joint motor design specifications. An electromagnetic analysis was performed during design using the two-dimensional finite element method, and the detailed dimensions of the motor were determined using the response surface method, which is an optimal design technique. The thermal characteristics of the joint motor were evaluated using a thermal equivalent circuit. The designed joint motors were manufactured, and their performance were tested not only at the component level, but also at the robot system level to verify experimentally the validity and usefulness of the proposed joint motor design method.

Thermal deformation of journal bearings operating under high-temperature conditions can have a significant effect on changes in bearing performance. However, no attempt has been made to quantify this amount of thermal deformation and link it to the performance change of the bearing. The aim of this study is to investigate the quantitative performance change due to thermal deformation of the tilting pad journal bearing (TPJB) pad in terms of the change in preload amount. The variable viscosity Reynolds equation and the energy equation were coupled using the relationship between viscosity and temperature, and the solution was obtained using the finite element method. Heat transfer between the spinning journal, oil film and pads is considered, and a three-dimensional (3D) finite element (FE) model was used to calculate the thermal deformation of the bearing structure. The steady state of the rotor-bearing system was predicted using a bearing performance prediction algorithm with three closed loops. State variables for this steady-state prediction include the amount of thermal deformation of the structure. In order to investigate the amount of thermal deformation of the bearing pad in terms of bearing performance, the concepts of thermal offset preload and thermal performance preload were suggested and the change in thermal preload under various conditions was investigated.

This paper presents the electromagnetic and thermal characteristics of a permanent magnet synchronous motor (PMSM) in a joint actuator which is used for articulated robot application. In an attempt to design a compact PMSM for the articulated robot, robot link should be taken into consideration during the motor design process as it can reduce the temperature distribution on motor, thus reducing the volume of the motor. A lumped-parameter thermal model of PMSM with and without a link is proposed considering the core loss, copper loss, and mechanical loss as heat sources. The electromagnetic and thermal analysis results are well confirmed by the experiment in a 400 W 20-pole/24-slot PMSM. The experiment results show that the robot link helps to reduce the motor end-winding temperature by about 40%, and this leads to an increase in power density of the motor.

The demand for electric bikes has been increasing in recent years, and so has their drive, which requires a high power-to-weight ratio or a high power density. An axial-flux permanent magnet motor with a Halbach-array is an excellent choice for electric bike drives thanks to its known characteristics of high power density, reliability, and efficiency. However, because an axial-flux machine topology is not common, the manufacturing process can be challenging, especially in the stator core. A good solution to this problem is to remove the stator tooth tips, as this simplifies the stator core shape and makes manufacturing easier. The proposed electric bike has limited housing dimension constraints; thus magnet sensors were implemented to support the Hall sensors in detecting the rotor position. The designed models were analyzed using the 3D finite element method (FEM) to determine their electromagnetic and thermal characteristics. A prototype was manufactured based on the final design and tested under rated conditions to validate the analysis results.