Motion analysis and control of the hybrid multi-DOF motor with taking account on design of motor shape

Abstract

There are many applications which need the multi-DOF system, such as robotics[1]- [4] . Generally, multi-DOF systems are comprised of many motors . Therefore, the systems are bigger and heavier because of these one more motors . It is not a problem using it in a large system like heavy industry, but a problem using it in a small system . For the multi-DOF motion in these small systems, the multi-DOF motor is the solution decreasing the system size . A multi-DOF motor has multi-DOF and it can be replaced one or more motors for multi-DOF motion . But a multi-DOF motor is complicated and difficult to control because it has many coils and magnets for the movement . The conventional multi-DOF motor is a spherical motor which shape is spherical for multi -DOF movement . However, the spherical motor has manufacturing and control problems, because of its shape . Therefore, it has poor performance such as low efficiency and torque[5]-[7] . This paper proposes new type multi -DOF motor called Hybrid multi -DOF motor . Unlike spherical motor, this multi -DOF motor has cylindrical shape . Also it has two separated motors to handle the rotating and tilting motion independently . The outer motor is used for rotating movement, and the inner motor is used for tilting movement . Fig . 1 . shows the hyrid motor and its two separated motors . Fig . 1 .(a) shows a hybrid multi-DOF motor . It is composed of an outer motor and an inner motor . The outer motor in Fig . 1 .(b) is for 1-DOF rotating motion and it is outerrotor type 3-phases BLDC motor . Also the design of the outer motor is not difficult because it is totally separated from the inner motor . Another motor in the hybrid multi-DOF motor is the inner motor . It is shown in Fig . 2 Fig . 2 .(b) Also, the coils is on the support plate(stator) and it is shown in Fig . 2 .(c) .The rotor and the stator are connected by an universal joint . The universal joint helps the 2-DOF tilting motion smooth . Meanwhile, two opposite coils and PMs can make same direction torque . In this paper, two types of inner motor are studied to improve the moving range and torque of the hybrid 3-DOF motor . Fig . 3 . shows two designed driving part of inner motor . They have same size of PMs and coils, but different shape of stator and rotor core . Both motor will be tilted by the direction and the magnitude of currents, but its torque and tilting range will be different as the core shape . The first type in Fig . 3 . (a) is normal type and its size of stator core is similar to the coil bobbin . On the other hand, the second type in Fig . 3 . (b) has extended stator core and additional rotor core between PM . Their performance is analyzed by FEA . In order to validate the FEA results, 2 types of motors are manufactured and its positioning control is performed . Fig . 4 shows the control system of hybrid 3-DOF motor . In the full length paper, the results of their performance will be shown by FEA(Finite Element Analysis) and experiments . The analysis results show the torque characteristic of these two...