An active damping system for a driveline includes a prop shaft configured to transmit engine power from an engine to a load, a sealed damper housing, and an active damping fluid contained within the sealed damper housing. A viscosity of the active damping fluid is changeable based on a torsional vibration of the prop shaft. The active damping system further includes a piston fixed to a side of the prop shaft and in communication with the active damping fluid. The piston is configured to rotate about an axis of the prop shaft. The system further includes a viscosity changing unit in communication with the active damping fluid, and a controller operatively connected to the viscosity changing unit. The controller is configured to cause the viscosity changing unit to change a viscosity of the active damping fluid. The viscosity of the active damping fluid changes the torsional vibration.

A main spindle device for a machine tool includes a main spindle, a cushioning member, and an arithmetic unit. The cushioning member is disposed on a position where a vibration displacement of a rotator exists. The arithmetic unit uses data of a tool to be used to analyze a vibration mode in a free vibration of the rotator based on a support rigidity of a bearing, masses of respective parts of the rotator including the tool, an attenuation coefficient, and an equation of motion derived from rigidity and inertia by a rotation. An outer diameter of a sleeve positioned outside the bearing is changed such that a position of an antinode of the vibration or a position on which a vibration displacement exists in the vibration mode matches a position of the cushioning member inside the main spindle to change a preload on the bearing.

A vibration damper having a cylinder filled with pressurized medium and a displacer that drives a generator. The vibration damper has a resilience element that compensates pressure peaks from the displacer movement relative to the generator. The resilience element is constructed as a torsion damper for the generator.