What is the Difference between a Piezo Actuator and a Programmable Piezo Shim?

New Tools for Design Engineers of Optics and Precision Mechanical Systems

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Piezo stack actuators have been used in applications such as photonics alignment, positioning, force generation, and fast valve actuation for several decades. They provide high dynamics, but can also be used for quasi-static applications due to their high-stiffness and stability.

The principle is relatively simple: the extension of the stack changes roughly proportional to the drive voltage, with typical strain on the order of 0.1% of the stack’s length available. Charging and discharging of a piezo actuator is related to charging and discharging an electric capacitor.

Basic design and typical displacement curves of standard open loop piezo actuators (w/o position feedback). Displacement is roughly proportional to the electric field and when the drive voltage is removed, the displacement reaches 0 once the element is fully discharged. More information on piezo motion and applications
Basic design and typical displacement curves of standard open loop piezo actuators (w/o position feedback). Displacement is roughly proportional to the electric field and when the drive voltage is removed, the displacement reaches 0 once the element is fully discharged. More information on piezo motion and applications

Quasi-Static Applications

When static applications are concerned, i.e. several parts are to be aligned and held in place, piezo actuators work well, and their atomic-level resolution is welcome in many optics, laser and semiconductor related applications. However, each actuator will require a driver to maintain the required position. When the voltage source is removed, the piezo stack will slowly discharge and whatever dimensional change was affected by charging it will disappear.

Programmable Shims

A new technology, also based on the piezo effect, can be utilized in situations where high resolution and stability are crucial, but a continuous drive voltage is unwanted and accessibility for manual adjustment is not possible.

Example of programmable piezo shim application
Example of programmable piezo shim application

Applications for programmable (semi-active) shims can be found where the alignment between two or more subassemblies is critical and realignment may be required at some point due to environmental changes, creep or settling processes, etc.

Examples:

  • Precision mechanical engineering
  • High-end optical assemblies for astronomy and semiconductor manufacturing
  • Material research test systems in synchrotrons

PIRest Technology

PIRest active shim technology is based on piezo ceramics and uses a hand-held programmer to change the displacement within seconds. Once a new position is programmed, the position is held stable to within nanometers over many days. These programmable shims can be made in virtually any shape and size such as plates or rings. Hybrid combinations with traditional piezo actuators for dynamic applications (e.g. vibration cancellation, precision motion control, etc.) are also feasible.

Hybrid combination of traditional piezo stack actuator (bottom, orange) and programmable shim (top, blue)
Hybrid combination of traditional piezo stack actuator (bottom, orange) and programmable shim (top, blue)

 

Nanometer Resolution

Since the piezoeffect allows for virtually unlimited resolution (which is why atomic force microscopes rely on piezo actuators), programmable dimensional changes in the nanometer range are feasible with the piezo shims.

Different programmed positions, show nanometer displacement, irrespective of the load.
Different programmed positions, show nanometer displacement, irrespective of the load.

 

Application of multiple programmable shims in an optics application. When settling or environmental effects in the optics/mount interface cause tension (= reduced surface flatness), programmable shims can fix imbalances and significantly improve the image quality.
Application of multiple programmable shims in an optics application. When settling or environmental effects in the optics/mount interface cause tension (= reduced surface flatness), programmable shims can fix imbalances and significantly improve the image quality.

 

Specifications

A variety of standard programmable shims are available as listed in the table below. Custom versions are possible.Specifications table

PIRest multi-layer programmable piezo shims, non-encapsulated ring version shown. PIRest multi-layer programmable piezo shims, non-encapsulated ring version shown.

 

Multi-Axis Arrangements

Bi-pod, tripod, and hexapod-type arrangements are feasible for multi-axis adjustments.

 

 

Learn more about PI Precision Motion Systems, Stages, Components: www.pi-usa.us/products/index.php

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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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