Piezo force generation
Piezo flexure actuators are used for precision positioning, moving things quickly, and force generation. Usually, force generation means pushing against an external elastic material. Working against a load reduces the available travel of an actuator, according to a simple formula for effective force that a piezo actuator can generate in a yielding restraint, where:
- L0 is the maximum nominal displacement without external force or restraint (m).
- kT is the piezo actuator stiffness (N/m).
- kS is the stiffness of the external spring (N/m).
The additional motion provided by flexure-amplified piezo actuators does come at a price. With increasing amplification ratio, both stiffness and responsiveness are reduced. Nevertheless, well-designed piezo flexure actuators can still provide sub-millisecond step-and-settle times, significantly faster than any other conventional actuator.
Custom actuators: no one-size-fits-all solution
With the variety of parameters such as size, force, precision, travel range, and cost, it is obvious that one flexure actuator cannot fit all applications. A standard part may come close enough to be integrated in a prototype. However, for optimized cost and performance, it usually pays off for the OEM mechanical system engineer to work closely with an experienced piezo mechanism manufacturer. Prototypes of custom designs can be prepared in as little as a few weeks.
100 billion cycles of lifetime: when failure is not an option
Regardless of the form factor, the latest designs of piezoelectric actuators are very reliable mechanisms. They must be, since they are the mission-critical heart of so many industrial and research applications, ranging from semiconductor fabrication to atomic-force microscopy. They are structurally quite similar to ceramic capacitors, which are ubiquitous in electronics.
Ease of use and cost effectiveness
Central to the utility of piezoelectric flexure actuators is their range of configurations and their well-thought-out mounting provisions. These are easy mechanisms to integrate into a design. Everything has been considered. Their integrated preload mechanisms accommodate even high-dynamic actuation. Their optional position sensors are pre-aligned and reproducible. Their flexure guidance accommodates common applications without difficulty. A wide range of controllers are available, spanning the spectrum of capability and cost. Some feature the latest communications interfaces, internal waveform-generation capability, all-digital servo-controlled (including trimpot-free) calibration, and integrated data-collection options, all in cost-effective, OEM-friendly configurations.
Expanding the spectrum of piezoelectric motion
Piezoelectric flexure actuators are but one utensil in a deep toolbox of motion technologies driven by piezoelectric principles, which include:
- Piezo ceramic stacks
- Packaged, preloaded stack piezo actuators
- Piezo flexure actuators
- Piezo linear motors with long travels and nanoscale position-hold stability, such as walking motors for high push/pull and holding force, ultrasonic resonant motors for high speeds, and incrementing inertial motors (stick/slip) for low cost.
Each of these piezoelectric tools extends the capability spectrum of piezoelectric motion -- a spectrum that has expanded dramatically in breadth and depth in recent years.
Piezoelectric flexure actuators offer unmatched ability to drop into a custom assembly. They provide fast, precise actuation without fuss and bother and with demonstrated reliability to extend into the many billions of cycles.
Recently introduced integrated flexure actuators offer a new level of convenience and performance for the designer. They come complete with stictionless lever amplifiers for long travel, built-in preloads for high-dynamic operation, and optional feedback sensors for high-performance servo-control.
Piezoelectric devices are increasingly being utilized by product designers and incorporated successfully into a widening range of applications where precision motion control is needed. These devices are compact, require low voltage, deliver high torque, exhibit short response time, generate little heat, are both nonmagnetic and vacuum compatible, and have few mechanical component parts to wear out and service. Now the latest generation of piezoelectric flexure actuators delivers an even broader product development capability for OEM designers.
Scott Jordan is director of NanoAutomation Technologies for Physik Instrumente, and Stefan Vorndran is vice president of marketing.