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Sensor Influence on the Precision of Piezo Positioning Stages

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The choice of feedback sensor is one of the key performance factors of a piezo positioning stage. Below is a comparison between the two most commonly used sensors. When the absolute positioning information plays a critical role in scientific results, researchers prefer capacitive sensors. When cost is most important and / or results are based on relative position, the more economical piezoresistive sensors are just fine. PI provides stages with both options plus a variety of other sensor choices as well, depending on parameters such as sensitivity, stability, dynamics, cost, etc. It is important to understand the application and how the positioning performance affects the results to recommend the sensor best suited to the application.

In addition to the sensor type, the controller concept also has a strong influence on performance parameters, such as settling, linearity, and bandwidth. Two basic controller types are commonly used with piezo nanopositioning systems: classical, analog servos (can have a digital command interface) and digital servos (can also have analog command interface). Learn more on analog and digital servo controllers.

Piezoresistive Strain Gauge Sensors (PRS) and Capacitive Dual Plate Sensors

Comparison of Piezoresistive and Capacitive Dual Plate Sensors

  Piezoresistive Strain Gauge Capacitive Dual Plate Sensor
General Low cost, high sensitivity High stability / linearity, high sensitivity
Principle PR sensor epoxy bonded to piezo element or part of a flexure. When the stage moves, the PR sensor sees strain causing a change in resistance. The change in resistance is interpreted as position change by the controller. Capacitive sensors measure movement of the stage platform directly by sensing the gap between moving platform and the fixed frame.
Type of Measurement Inferred measurement Direct measurement
Best for High resolution positioning / scanning with relative movement requirements High resolution positioning / scanning where long term stability, absolute position, and repeatability are critical
Immunity to external electric noise Fair (DC output signal) Best (RF signal with high precision fixed-frequency reference)
Relative Cost Low cost About $1000 per axis higher than PR due to additional, higher precision mechanical and electronics components
Temp. sensitivity Fair Very low
Bandwidth Very Good Very Good
Parasitic errors No compensation possible Compensation possible
Long-term pos. stability Fair. The sensor is bonded to a surface that is bent or stretched. Basically, the sensor floats on a thin film of epoxy. If stain is added, drift in the nanometer realm will occur. Piezoresistive sensors are semiconductors and temperature changes have a significant effect. Nanoscale over 30min. There is no strain on the sensor and no contact.

Stability Record

A new stability record with sub-nanometer drift was recently achieved by the National Institute of Standards (NIST). The published article describes a complex dual laser beam-based measurement system. The experiment setup employs an XYZ piezo stage with capacitive position sensors, model P561.3DD from PI.

Schematic of back-scattered detection (BSD) apparatus (Image: JILA/NIST, https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-23-13-16554&id=320397)
Schematic of back-scattered detection (BSD) apparatus (Image: JILA/NIST)

The PInano piezo scanning microscope stage is available with both piezo-resistive and capacitive feedback.spacer(1)An applications article of the PInano P-545 XYZ stage (pictured left) in high resolution microscopy can be found is here:

“Continuous-Wave STED Microscope for Imaging Actin Cytoskeleton in Fixed and Live Cells”

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> READ Influence of Digital vs. Analog Control on Nano-Positioning Performance

> READ Nanopositioning Applications in Nanoscopy

> WATCH “Nanopositioning: Why Parallel-Metrology is Better” video

> LEARN more on PI-USA website

> READ more articles

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About PI

PI (Physik Instrumente) is a leading manufacturer of precision motion control equipment, piezo motors, air bearing stages and hexapod parallel-kinematics for semiconductor applications, photonics, bio-nano-technology and medical engineering. PI has been developing and manufacturing standard & custom precision products with piezoceramic and electromagnetic drives for 4 decades. The company has been ISO 9001 certified since 1994 and provides innovative, high-quality solutions for OEM and research. PI is present worldwide with fifteen subsidiaries, R&D / engineering on 3 continents and total staff of more than 1,000.

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