open loop mode: 100% motion - closed loop mode: 80% motion

Why can I reach in closed loop operation only 80% of the motion in open loop operation?

When piezo actuators with a measurement feedback system are operated in closed loop, the full motion will not be available.The control system needs a voltage buffer to reach the specified critical limits of the zero point and the maximum motion in the specified control response time. The decrease of the motion is approx. 20% of the overall value.