How do you achieve “closed-loop?”
Our nanopositioners use piezo actuators to generate motion. The expansion of a piezo actuator is normally proportional to the driving voltage. In an open-loop system a linear voltage is applied for motion control. However, piezo actuators exhibit nonlinearity, hysteresis and creeping, which will be translated as positioning errors in the positioning system. The term “closed-loop” in nanopositioning indicates that a position sensor is used to monitor the position of the stage in real time and feed back the readings to the controller for error correction. It guarantees that the nanopositioner reaches its precise commanded position. The position sensor is most commonly a capacitor, a LVDT or a strain gage. The control electronics are either analog or digital. nPoint nanopositioners use capacitor sensors coupled with digital control electronics to achieve closed-loop control.