Control for elliptically polarizing undulator at SRRC

A Sasaki-type elliptically polarizing undulator (EPU) which will be an important project of insertion device at SRRC is in the construction phase. It can produce an elliptically polarization for advance study in soft X-ray region. The precision of phase is main issue for this control system. The loads of the motor drivers vary with different magnetic force which results from changing the phase and the gap position to result in affecting positioning precision. For minimizing the steady state error and getting a better tracking performance, the parameters of the control loop art necessary to optimize. The control system provides the functions so beamline users can adjust gap or phase. The graphical user interface provides a easy operation interface for operators. The details of the EPU control will be presented in this report.