Vibration reduction techniques for stepper motors at standstill in high precision applications

Stepper motors are widely used in high precision positioning applications where reliability is an important factor. Field Oriented Control (FOC) can be used to damp the high-oscillatory dynamics of open-loop driven stepper motors and effectively reduce induced vibrations during motion. However, when it is required to hold a constant position, the induced vibrations can be higher in FOC than in open-loop control. To solve this, different techniques are proposed in this paper: i) a bump-less switch from FOC to open-loop control, ii) reducing the current reference to zero and iii) reducing the applied voltage to zero. Unlike other studies in vibration reduction techniques based on motion regimes and online feedback, the techniques presented here successfully reduce the vibrations in standstill and without the use of additional sensors. These methods are applied to a crystal collimator at CERN with good results and their performance is compared.