Abstract
Since direct drive (DD) motors have high stiffness and no backlash, they can realize precise position control. However, DD motors are easily affected by the disturbance and the parameters variation compared with motors with reduction gears. To suppress the effect of disturbance, the disturbance observer which estimates the total disturbance of motors from torque current and speed or position signal has been proposed. The feedback of the estimated disturbance makes the motors robust against the parameters variation and the disturbance, and requires less calculation effort. The disturbance compensation by the disturbance observer is a realization of two-degrees-of-freedom control system. First, we analyze the characteristics of the system with the disturbance feedback and realize acceleration control. Next, a controller which realizes desired response of position, speed and acceleration is constructed based on the acceleration controller. Finally, the continuous path control is performed by a linear synchronous motor which is a kind of DD motor. The disturbance is estimated by an observer whose input is torque current reference and position signal. Robust and precise control with micron order accuracy is realized experimentally.
