What does open loop and closed loop mean?
Actuators are prerequisite and they must have a clear dependency between input value and position. This is, for example, the case for stepper motors or Piezo stack actuators. Advantages are also the sturdiness and lower costs of such a system. Open loop systems are specifically used for external interferences (vibration, shock) and changing loads.
For closed loop systems, the actually reached position is measured and compared periodically with the desired position. The controller moves the actuator by the shortfall and tries thus to balance the fault. A higher accuracy is achieved and changeable temperatures are balanced out. Disadvantage of all closed loop systems is the risk of instability of the control loop which becomes noticeable by the vibration of the system.