Characteristics Analysis of the Motions of the 2-Degree-of-Freedom Direct Drive Induction Motor

The 2-degree-of-freedom direct drive induction motor (2DoFDDIM) is capable of implementing rotary, linear or helical motion, which has the definite advantages of integrated structure, high material utilization and so on. In this paper, the characteristics analysis of the three kinds of motions are presented. The air-gap magnetic field distributions and mechanical characteristics of the 2DoFDDIM with three motions are derived respectively. The results show that there is super synchronous speed or velocity phenomenon for rotary or linear motion. Moreover, the coupling effects between the rotating and travelling wave magnetic fields, and that between the two mechanical motions will deteriorate the performance of 3D helical motion compared with 2D motion (rotary or linear). The expressions of the resistant torque and force caused by the coupling effect are derived, which are verified by 3D finite element models (FEMs). The results regarding to the weakening of the output torque of helical motion and interacting magnetic field obtained from FEMs are then verified by experimental tests. Finally, the skewed slot method is applied to 2DoFDDIM, which successfully improves the performance of helical motion aiming to compensate the coupling resistant torque and force.