How to Amplify Piezo Motion?
Mechanical amplification methods for piezoelectric actuators are crucial for enhancing their displacement capabilities. Lever mechanisms, for instance, use a simple principle of fulcrum and lever arms, converting the small displacements of the actuator into significantly larger movements. Flexure mechanisms, on the other hand, employ flexible structures that bend and flex to amplify the motion, often used in precision engineering due to their high accuracy. Gear trains can also be employed, where the rotational movement of the actuator drives a series of gears, resulting in a larger linear displacement. Lastly, compliant mechanisms, designed to flex at specific points, can amplify the displacement through their structural configuration, making them ideal for micro-positioning systems. Each method offers unique advantages, making them suitable for various applications requiring amplified movements from piezoelectric actuators.
In precise systems, flexure or compliant mechanisms offer more advantages. First of all, they can achieve highest repeatability. The lack of joints and moving parts means there is no backlash or wear, leading to more consistent and repeatable motion. Make sure they operate in elastic region and you can accurately estimate their motion under certain input force. You can use strain gauges to measure the deformation with sub-nanometer precision and resolution. Moreover, having no moving parts eliminates the need of lubricants so they are more suitable to use in vacuum or cryogenic environments.
Some of the popular types of amplified piezoactuators using flexure and compliant mechanisms.
Realizing amplified motion of piezoactuators requires sophisticated design. Piezoactuators are fragile components, they may crack or chip at locations where stresses are concentrated. They are also weak in tension loads, so one must ensure that only compressive loads are applied on piezoactuators during operation. Adequate preload on piezoactuators are curicial in especially when moving large masses in high frequencies to prevent tension loads. Also, termal expansion needs to be taken into account. Some piezoelectric materials have negative thermal expansion coefficient. That means when it is bonded to a metal surface, it contracts while the metal surface expands. When it is not properly handled, thermal stresses could lead failure of piezo or other components.
Stresses on the other parts of compliant mechanisms are also need to be analyzed properly. Plastic deformation shouldn't be allowed in most cases, as it may lead to failure. Also, having stresses near yield limit means deformations might be non-linear and that might cause inaccuracies in the positioning systems. Dynamic behaviour of the components should also be analyzed to prevent shock or vibration damage on materials. Even when stresses caused from static loading are much below the yield stresses, fatigue may occur when there is high frequency vibrations. Considering piezoactuators are mostly used to realize high frequency movements, materials should withstand millions or even billions of load cycles.
Stiffness of the materials should be taken into account when designing amplified piezo actuators. Ideally, an amplification structure should deform easily with the input force to ensure the displacement is not hindered but also provide enough stiffness so it can provide enough output force. The mechanism should be optimized to provide the desired output displacement and force according to the application. For example, one application may require large amplification ratios but the exerted force may not be important if the load is very small. But if a large body should be moved in high frequencies, having enough stiffness is crucial.
Stresses on a rhombus type motion amplifier. Finite Element Analysis is an important tool for designing amplified piezoactuators.
Designing amplified piezoactuators are not the end of the hassle. Their production and assembly is also another challenge. Most of the time, piezoelectric devices are tiny. Moreover, compliant mechanisms have thin deformable sections act as linkages. These thin sections are not always machinable with traditional milling machines because the material might deform under cutting forces. Electrodischarge machining (EDM) is one of the preferred methods for producing such intricate details thanks to the non-contact material removal by creating spark with a thin wire.
Intricate details on hard materials can be manufactured by electrodischarge machining (EDM)
Designing and manufacturing amplified piezoelectric actuators are challenging when you need to achieve highest performance. Ulsis has designed many different types of it, you can check out our products . If you cannot find the best product for your application, you can contact us to discuss about what you need and collaborate.
