Review of Nanopositioning Systems Actuators and Sensors
Today many fields in research and industry require motion control with very high precision in the sub-nanometer range. Semiconductor test and metrology applications rely on nanopositioning equipment and all branches of optical microscopy, scanning electron microscopy and atomic force microscopy, white light microscopy, interferometry, near field scanning microscopy and super resolution microscopy can only move forward through the continuous progress in nano motion control technology.
In the field of photonics and laser technology, tunable lasers rely on the performance of nanopositioning actuators to stabilize cavities, or to position diffraction gratings with extreme precision and repeatability. The virtually unlimited resolution and extremely fast response of piezo stack actuators is very desirable in these applications and new piezo walk nano motors provide essentially unlimited travel ranges that allow gratings to be moved over longer distances.
To make best use of the high resolution provided by piezoelectric motion, traditional mechanical guiding systems are not acceptable. Instead, flexure guided mechanisms are state-of-the-art. Multi-axis guiding systems (parallel-kinematics) together with multi-axis sensors (parallel metrology) are now available. The highest precision sensors are based on the capacitance principle, because it measures directly and without contact. In addition there is no drift and no Johnson Noise as seen with lower-cost strain gauge type sensors such as semiconductor piezoresistive sensors and thin film strain sensors.
Parallel-kinematics designs are based on only one moving platform, a great advantage over the traditional serial designs where each axis has its own platform with its own drive and sensor. Because each sensor can only see input from its own axis, all errors caused by the other axes in the system cannot be seen and “reported” to the closed-loop controller. For example, if the Y-axis produces some runout motion in X due to guiding errors or due to external forces, the controller cannot react to it, because the X-sensor is mounted on the X axes and will not see it. In a parallel-kinematics / parallel-metrology design, all motion (no matter where it originates from) is seen by the X sensor, because there is only one common motion platform.
Each nanopositioning stage and actuator not only relies on the precision of its mechanical design, but also on the performance of the closed-loop controller. Digital piezo nanopositioning controllers improve the linearity and precision significantly over the still more widely used analog servos. The digital servo also allows fast adaptation to changing load / settling / speed requirements and simplifies tuning from the controlling computer. The digital servo is not to be confused with a digital interface that is available on most analog servo controllers. High-end digital controllers also come with analog input interfaces to simplify the adaptation of control signals that are already available in analog form, such as those from function generators, autofocus sensors or PSD (position sensitive diodes).Controllers from reputable suppliers come with software drivers and programming examples for all common environments to allow for seamless integration of the nanopositioning system into the customer’s application.
Piezo - About Author:
Technology has always fascinated the technician inside me. And writing about the latest in technologies and mechanisms in usage has been my forte over the last few years. Follow my write ups to know about the latest in technologies and mechanisms this season for one. This fall Nano positioning systems are very much in demand among the technical and mechanical industries across the world. Keep yourself updated on these products exclusively from USA.
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