Piezo Actuator Basics

Overview of Piezo Actuator Working Principles

Piezoelectric ceramic materials are an electro-active ceramic. “Piezo-ceramics” expand/contract with applied electrical charge. When assembled into a piezo stack (many parallel layers), applied control voltage effects travel on the order of 0.1% to 0.2% of the piezo stack length. In piezo actuators, this travel becomes useful as actuation work (power) for a variety of applications. Piezo stack linear actuators might be considered as expanding springs, able to provide force and displacement as the control voltage drives them to expand/contract. This piezo actuator tutorial covers how piezo actuators work, the major application benefits, flexure-guided actuator properties and characteristics, frame architectures, travel, force, frequency, and how to select a piezo actuator for your application.

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Major Application Benefits of Piezo Actuation Systems

  • Premium Force-to-Weight Ratio
  • Significant Power-to-Volume Ratio
  • Flexure-Based Yields Zero Backlash
  • Wide Bandwidth Operation
  • Sub Nanometer Proportional Displacement
  • Extreme reliability (billions of cycles)
  • No Lubrication
  • Solid-State Design Reduces Component Count
  • Nonmagnetic Construction Possible
  • Vacuum Compatible

Introduction to Flexure-Guided Piezo Actuator Properties

DSM standard LFPA piezo actuator with 10 mm travel
10mm Travel LFPA Actuator

The active piezo stacks in DSM’s piezo flexure actuators are located in the center of a surrounding flexure-frame. DSM’s flexure-frames provide mounting options to guide travel, compressive preloads to protect the piezo ceramic, and solid-state flexures to enhance response. To mechanically amplify the small piezo travel range, DSM’s amplified flexure-frames use kinematic levers to amplify travel up to 10 mm. Since output travel is controlled directly by input voltage, piezo flexure actuators provide proportional displacement response. Solid-state flexures within DSM’s actuator frames provide quiet, lubrication-free, vacuum compatible and nonmagnetic travel possibilities.

Flexure Piezo Actuators Customizable To Your Application

Standard available flexure-frame actuators from DSM are created using a design process that addresses a wide range of functionality and environmental specifications. Four basic actuator types are available in the Non-Amplified, Flextensional, Levered, and High Frequency architectures. While a number of standard options are available within the four types, a majority of DSM’s actuators are uniquely designed to specific customer requirements. Please contact DSM’s design and application engineers to request a review of your specific requirements.

Non-Amplified Actuator (NA)

Custom NA-80 piezo actuator vacuum/high temperature compatible
Custom NA-0080 Vacuum/High Temperature Compatible
High resonant frequency and high force capability.

Non-amplified actuators use a direct-drive design leading to higher resonant frequencies than mechanically-amplified piezo actuators. Piezo material expansion directly creates output travel. The flexure-frame provides beneficial preload and convenient mounting options. NA actuator flexures are designed to minimize preload frame impedance to the piezoelectric travel and increase the actuator’s stiffness. Compressive preload enhances tolerance to external loads. Some specialty NA actuators may support compressive/tensile load to >2000 N.

Flextensional Piezo Actuator (FPA)

FPA is typically the most efficient mechanism for converting piezo energy to actuator work. Standard nominal travel values are 50 µm to >2000 µm.

DSM standard FPA-0200C piezo actuator
Standard FPA-0200C Actuator

The Flextensional Piezo Actuator (FPA) is an optimal configuration for mechanically amplified piezo actuators. DSM’s flexure-frame uses carefully designed flexures and preload bands which leads to greater conversion of piezo energy to output work. An amplified flexure-frame is a solid-state mechanism which means that there are no traditional pivots within the device. The flexure, also known as a living hinge, enables rotation while limiting play in the mechanism.

 

The FPA geometry consists of a central piezo stack compressed by preload bands between two solid endcaps. Kinematic flexures connect the endcaps to flextensional arms and to the output blocks. DSM offers both energize-to-expand and energize-to-contract FPA geometry. When the piezo is energized, the output blocks expand away or contract toward the frame center.

DSM FPA piezo actuator diagram

FPA geometry is available in single-arm or double-arm construction to provide additional output guidance stability. In double-arm construction, the extra set of arms reduces the potential for output block rotation. DSM’s range of FPAs offers a wide selection of open-loop displacement, stiffness, blocking force and resonant frequency.

 

The preload bands in DSM’s actuators especially enhance the actuators ability to carry compressive and tensile loading. The preload level is carefully designed to limit the potential for the endcaps to separate from the piezo stack under allowable operating conditions. If loading has the potential to drive the endcaps away from the piezo stack (e.g., when the FPA is "overloaded" in the direction of its designed travel instead of opposite), the preload holds the piezo stack in contact with the actuator frame. When applications require significant loading in the same direction of travel, DSM may customize the actuator design with additional preload elements.

 

Piezo actuator flexure-frames can be made from nonmagnetic materials for high magnetic field applications. Piezo actuators can be used for cryogenic and vacuum applications. Composite frame materials can be implemented where weight savings is crucial.

Lever-Amplified Piezo Actuator (LFPA and LPA)

Simple lever mechanism lowers moving mass to promote higher resonant frequency.

Lever-amplified piezo actuators (LPAs) may have a higher natural frequency than a Flextensional Piezo Actuator (FPA). Using a simple design geometry of a classic lever and fulcrum, the piezo stack provides the applied force or displacement to move the output load. Using the simple lever geometry, the output arm may be designed with a lower moving mass than other amplified actuator types. With less moving mass, the actuator output resonant frequency may be higher than a comparable FPA actuator. The LPA series has clear access to both sides of the actuator output, which can be beneficial. It also offers access to both sides of the stack, which allows creative enhancements such as the addition of a radiation shield or additional sensors.

 

LPAs can have a two-stage amplification mechanism as in the Lever-amplified Flextensional Piezo Actuator (LFPA). The combination of two amplification stages can provide a large nominal travel value up to 10 mm in a mechanical volume less than 20 x 50 x 100 mm. LFPAs and LPAs can be configured to expand or contract when energized.

DSM standard lever amplified fpa piezo actuators (LFPA)
Standard Lever-amplified FPA Piezo Actuator (LFPA)

High-Frequency Piezo Actuator (PSA)

Higher resonant frequency than FPA's and greater stiffness than LPA's, PSA's may provide a beneficial compromise.

DSM custom PSA piezo actuators configured in a high speed piezo shutter assembly
Custom PSA Actuators configured in a high-speed piezo shutter assembly

PSA nominal travel ranges from 200 to 1500 µm with corresponding resonant frequencies greater than 3 kHz and 600 Hz, respectively. A wider bandwidth of operation is possible with PSA actuators than other flexure-based actuation technology. Since these actuators have a lower moving mass, they have a greater resonant frequency for comparable actuator stiffness values. The PSA series’ significant displacement with resonant frequency greater than FPA actuators makes them suitable for shutters, high-frequency valves, switches and high-speed industrial automation.

How to Select a Piezo Actuator for your Application

To aid in selecting a piezo actuator type, DSM has developed the following considerations. Responses will drive the selection of a piezo actuator type to address a wide range of performance factors. Email DSM's application engineers at salesinfo@dynamic-structures.com to interact regarding these topics.

  • Action or function of piezo actuator
  • Nominal travel required, with and without safety factors
  • Magnitude and type of load (mass versus spring versus friction)
  • If it is a static mass load, will additional dynamic load (spring force) be required?
  • Positioning resolution required
  • Positioning accuracy required
  • Bandwidth requirements, piezo actuator speed or drive frequency
  • Desired motion profile (point-to-point, sinusoidal, etc.)
  • Open loop operation or closed loop servo control
  • Are there any special environmental considerations (temperature, humidity, vacuum, etc.)?