Nanopositioners, Piezo Positioners, Nanopositioning Systems
PI has 4 decades of experience in nanopositioner design & manufacture. With 700 employees and R&D and manufacturing on 3 continents, PI is the global leader in nanopositioning systems and piezo stages.
Capacitance sensors are the nanometrology system of choice for the highest precision nanopositioner designs.
Single probe capacitive sensors are more versatile and dual probe capacitance sensors ensure higher linearity and longterm stability.
These absolute-measuring, non-contact sensors detect motion at sub-nanometer levels directly (direct output metrology)
and provide accuracy, linearity, resolution, stability and bandwidth superior to strain gauge type sensors (piezo resistive
sensors), LVDT sensors and incremental encoders (glass scale type encoders). If used in parallel-kinematics multi-axis systems,
they can also provide the information for automatic runout-compensation.
Minimized recoil forces are a by-product of the ultra-low-inertia approach. Classical Micropositioning stages, even when equipped
with high-resolution encoders cannot achieve this precision.
Their high inertia, friction, and servo dither prevent fast motion at the nanometer level.
Flexure motion is based on the elastic deformation (flexing) of a solid material.
Friction and stiction are entirely eliminated, and flexures exhibit high stiffness,
load capacity and resistance to shock and vibration. Flexures are maintenance free
and not subject to wear. They are vacuum compatible, operate over a wide temperature
range and require neither lubricants nor compressed air for operation.
Not all flexures are created equal! PI multi-axis nanopositioner systems are based on
FEA calculated wire-EDM-cut parallel-kinematics flexure designs.
These multilink flexure guiding systems eliminate cosine errors and
provide bidirectional flatness and straightness in the nanometer or microradian range.
This high precision means that even the most demanding nano-positioning tasks can be run bidirectionally
for higher throughput.
Wire-EDM cutting process
provides highest-accuracy flexure guiding systems in compact nanopositioning piezo stages.
Typical 0.5 µrad bidirectional trajectory repeatability (P-752.11C
flexure nanopositioner Piezostage) means processes may be performed bidirectionally for twice the productivity
PI piezo nanopositioner stages employ the award-winning PICMA® piezo actuators, the only actuators with co-fired
ceramic encapsulation. The PIMCA® piezo technology was specifically developed by PI’s piezoceramic division to
provide higher performance and lifetime in nanopositioner applications.
Multilayer piezo actuators are similar to ceramic capacitors and are not affected by wear and tear.
PI nanopositioner systems are designed to be driven at lower voltages than most other piezo systems (100 V vs. 150 V).
The research literature, PI’s own test data and 30+ years of experience, all confirm that lower average electric fields
lead to longer lifetime.
Active Trajectory Control is avail- able on single-module parallel-metrology nanopositioning systems.
It can improve straight- ness and flatness to sub-nano- meter precision. Digital control- lers with advanced
coordinate transformation algorithms allow active trajectory control for up to 6 DoF.
Active Trajectory Control significantly improves guid- ing precision.
It requires a Parallel Metrology Sensor setup.
Elliptical scan in a laser micro-drilling application with XY scanning piezo stage,
conventional controller. The outer curve describes the target position,
the inner curve shows the actual motion of the piezo stage.
Same scan as before, with Dynamic Digital Linearization.
The tracking error has been reduced to a few nanometers, real and target
positions are indiscernable on the graph
Preshaping™ algorithms and dynamic digital linearization can increase the dynamic linearity and effective
bandwidth of high-speed nanopositioner systems by up to 3 orders of magnitude. This translates into higher
dynamic accuracy, and increased throughput.
Conventional PID (proportional-integral-derivative) piezo servo-controllers cannot
completely eliminate phase lag and tracking errors (the difference between actual and target positions) in dynamic operation. This is due to the
nonlinear nature of PZT material, the limited control bandwidth, and the fact that a PID controller needs to see an error before it attempts to correct it.
DDL (an option for PI digital controllers such as the E-710) solves this problem. This PI-exclusive technology reduces phase lag and
tracking error (the difference between the commanded position and actual
position) in dynamic applications to virtually indiscernible levels. The result is an improvement in dynamic linearity and usable bandwidth of up to three orders of magnitude. Dynamic Digital Linearization works both in single-axis and multi axis applications (see graphs).
The example above shows ringing of a poorly damped component on a high-speed nanopositioner stage.
While the closed-loop piezo nanopositioner stage settles perfectly, the component cannot keep up. Conventional
solutions to this problem would involve slowing down the piezo nanopositioner stage. Mach™ eliminates ringing without sacrificing speed.
It does not even require retuning of the servo system.
The exclusive Mach™ Throughput Processor™ eliminates resonant ringing, allowing rapid motion without a
settling phase.This technique also eliminates resonances excited in neighboring components, outside the
piezo nanopositioner system's servo loop. The result is significantly increased throughput.
Self-generated vibration affects:
The load and fixturing that
the nanopositioner actuates
The supporting structure on
which the nanopositioner is mounted
All other components attached
to the supporting structure
The example above shows vibrations induced at the beginning of a saw-tooth scan, typical in image acquisition applications. The vibration results in lower image quality. Mach™ improves the image quailtiy; there is no need to reduce the scanning frequency or chang the mechanical components in the system.
Mach™ is available as a firmware option for several PI Digital Piezo Controllers and also as an upgrade option for analog controllers.
This technology is protected by one or more of the following US
and foreign Patents licensed from Convolve, Inc.: US 4,916,635; US 5,638,267;
0433375 Europe; 067152 Korea, and other Patents pending. Mach™, Throughput Coprocessor™
and NanoAutomation® are trademarks of Polytec PI, Inc. Input Shaping™ is a trademark of Convolve, Inc.
* Ask about custom sizes, sensors or special designs.
Capacitive and LVDT sensors are direct metrology devices.
Capacitive sensors provide the highest accuracy, bandwidth and linearity.
Introduction to Piezoelectric Nanopositioning Actuators (Nano-Transducers)
Piezo Actuators (PZT) are ultra-high-resolution Nano-Transducers for a variety of applications from Nanotechnology
to Aerospace, Biotechnology and Medical Design. PI offers the largest selection Piezo Actuators and Translators (linear actuators) worldwide, for scientific and and industrial applications.
In addition to the hundreds of standard models, we manufacture custom designs tailored to customers’ requirements. PI is highly vertically integrated, controlling each manufacturing step from piezo raw materials to finished systems.
* Ask about custom sizes, sensors or special designs.
** Preloading increases tensile force capacity
SGS = high-resolution strain gauge sensor LVDT = Linear Variable Differential Transformer
Further information about piezoceramics can be found in the PI Ceramic catalog or at www.piceramic.de.