This work presents a method to move a vertical drillstring off-bottom in a given time without exciting the torsional vibrations. The control algorithm was originally developed for robots with flexible arms, and it is here applied to a long drillstring. The control strategy consists of calculating a feedforward torque based on the modal characteristics of the drillstring. The approach presented can be used to change the downhole orientation or to bring the drillstring to a stable rotational speed without residual vibrations before drilling is started. Numerical examples are presented for both displacement and velocity control strategies.

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