In this work, a magnetically suspended direct drive robot joint is developed, which is driven by a built-in torque motor. The active magnetic bearing system consists of two conical-shaped radial bearings for five axes active control of the shaft. The axial and radial displacements are controlled by DC and AC currents of the coupled PD controller.
The effectiveness of the control algorithm is validated through numerical simulations based on analytically derived nonlinear and linearized models. The dynamic response characteristics and stability of the closed-loop system, based on a five degrees-of-freedom linear system model are investigated with the control gains varied.
Experiments are performed to investigate the dynamic characteristics of the system while the torque motor drives the system at 0.45, and 240rpm. It is found that the system is successfully suspended with the steady state error less than ±1㎛. Comparison between the experimental and simulation results shows that modal parameters estimated from analysis and experiments agree well within the error less than 10% and that the motion of the magnetically suspended direct drive robot joint can be well predicted by the analytical work.