When it comes to specifying performance parameters of positioning and measuring devices for moving and measuring to nanometer precision, one immediately comes across the problem of defining what one actually means by various terms in common usage.  What is accuracy? Is it the same as precision? Is non-linearity the same as linearity? What reference plane do you take to define roll, pitch and yaw? Of course, many international standards have been written to help sort this out, and indeed they do help.

 

In NanoPositioning applications one great advantage of such materials

is the combination of sub-atomic resolution (picometre or below) with

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very high mechanical stiffness. This advantage outweighs their primary

disadvantage which is their extremely limited range. The maximum

strain achievable is typically 0.1% for reliable operation, about 1000

times greater than quartz. Thus, a device with 100 mm range would have

to be 100 mm long. To reduce the operating voltage to a low level, these

devices are manufactured in stacks of very thin layers. For example, a

20 mm long stack might have 200 layers each 100 mm thick, and expand

by 15 mm for 100 V. Typically these layers are produced using the tapecasting techniques developed for the manufacture of capacitors. Such a

stack is typically very strong in compression and able to generate a

force of about 750 N. This high stiffness results in very high resonant

frequencies, enabling devices to move at high speed in a controlled

manner. Because they can generate high forces it is also possible to

amplify their motion mechanically at the expense of lower frequency

operation.

 

By using NanoSensors to monitor the movement of mechanisms and

translators it is possible to servo-control the position of these devices

to sub-nanometre precision. A business must consider closely the nanopositioning software for sale on the market today.  A simple example of this is the Digital Piezo Translator. Here the motion of the PZT is monitored by the capacitancemicrometer. Any hysteresis, drift or creep in the length of the PZT is monitored by the sensor. The output of the sensor is then used to

control the voltage on the PZT to form a closed loop system. In this

manner the DPT achieves sub-nanometre reproducibility and deviation

from perfect linearity of 0.05%. More complex mechanisms combine

several axes of motion, along with mechanical amplification of the PZT

motion. In order to minimise parasitic motions, i.e. motion which is not

purely along a single dimension, and to ensure that these motions are

orthogonal, flexure mechanisms are used. Optimisation of these designs

is quite complex, requiring advanced design tools and extensive prototyping. These NanoMechanisms include NanoSensors on each axis to ensure sub-nanometre precision.

 

The role of a nanopositioner is to move to or position a probe, part, tool, sample, or device at some desired position with nanometer accuracy and repeatability. The positioner should also be able to resolve adjacent positions that are separated by less than a nanometer. Your business, such as Life Sceience/Microscopy, Semiconductor/Data Storage, Optics Development, AFM/Material Sciences or Photonics Packaging/Communications may need to learn more about nanopositioning solutions that would boost your productivity and accuracy.

Posted by Alice Stevens

Full time stay at home mom with three children. I love to blog!

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