Precision positioning technology has been widely used in precision manufacturing, scanning microscopy, semiconductor and other fields, and put forward higher requirements in terms of positioning accuracy, resolution, and response time.

Piezoelectric nanopositioning stage uses piezoelectric ceramic as the driving source and adopts frictionless flexible hinge guiding mechanism. It has the characteristics of high positioning accuracy, high rigidity, fast response speed and high resolution. It has become the core device of precision positioning technology. However, due to the hysteresis and creep characteristics of piezoelectric ceramics, the accuracy and stability of the positioning system are seriously affected.

Hysteresis

There is a displacement difference between the piezoelectric ceramic boost curve and the buck curve. Under the same voltage value, there is a significant displacement difference between the displacement values on the rising curve and the falling curve, and this displacement difference will change with the change of the voltage variation range. The smaller the driving voltage, the smaller the displacement difference will be. We define the slope between the switching points of the local hysteresis curve as the piezoelectric large signal deformation coefficient d_(GS):

Creep

Creep means that when the voltage applied to the piezoelectric ceramic does not change, the displacement value does not stabilize at a fixed value, but changes slowly with time, and the stable value is reached after a certain time.

In order to reduce or eliminate the influence of the above characteristics on the positioning accuracy of the piezoelectric nanopositioning stage, the closed loop system control can be selected for correction.

Closed loop correction

Closed-loop system uses the sensor to detect the position, and the controller corrects the detected offset by the voltage. Therefore, the closed-loop system has no hysteresis or creep problem. CoreMorrow closed-loop sensors are mainly used in three types: SGS, LVDT and CAP depending on the positioning accuracy requirements.

An example for CoreMorrow P66 piezoelectric nanopositioning stage:

Closed-loop version of P66 piezoelectric nanopositioning stage is equipped with high-resolution and fast-responding strain sensor (SGS) that is placed in the appropriate position of the drive mechanism to feed back high-bandwidth, high-precision voltage signals to the controller. The sensor uses a full-bridge configuration to eliminate thermal drift, resulting in a closed-loop linearity of 0.1% F.S.

P66.X30S closed loop linearity curve

CoreMorrow piezoelectric stage are available in closed-loop version, with closed-loop control system. The piezoelectric controller performs real-time correction of the displacement by PID algorithm for voltage adjustment, achieving nano positioning accuracy, good stability and high relibility.