DuraActパッチトランスデューサーのテクノロジー

製造

DuraActパッチトランスデューサーの活性層は圧電プレートで構成されています。これらのプレートは特許取得済みプロセスにより繊維強化プラスチック(GRP)に埋め込まれ、接着され合成物を形成しています。この積層プロセスは、注入法を用いて真空環境にてオートクレーブ内で行います。これにより、最高の品質を持ち気泡のまったくない積層板が得られます。

オートクレーブの硬化温度は、各使用材料の熱膨張係数からピエゾセラミックプレート内部に規定のプリロードが生じるように選択します。また、GRPのポリマーコーティングは、絶縁体および力学的プリロードの役割も果たします。この特許技術により、大量製造可能で頑丈であり、折り曲げられるトランスデューサー素子を実現しています。

Design & Production

The active layer in DuraAct patch transducers consists of one or more piezoceramic plates with metallized surfaces for electrical contacting. These plates typically measure between 200 and 500 μm in thickness. They are embedded in fiber-reinforced plastic (GRP) using a patented process and bonded to form a composite. The bonding process is carried out in an autoclave in a vacuum by means of an injection process to produce completely bubble-free laminates of the highest quality.

The curing temperature profile of the autoclave is selected so that a defined mechanical preload of the piezoceramic plates will result due to the different thermal expansion coefficients of the materials involved. The polymer coating of the GRP also serves as electrical insulation. Robust, bendable transducer elements that can be manufactured in large batches are the result of this patented technology.

DuraAct patch transducers are solid body actuators without moving parts. This means that wear and failure proneness are minimal. The electrical connection is made via two contact points to which wires can be soldered, glued or clamped, depending on the application.

How Do DuraAct Patch Transducers Work?

The piezoceramic plates that are used in all-ceramic DuraAct patch transducers are structurally similar to a capacitor. The ceramic serves as a dielectric between the metallic surfaces of the ceramic, which form the electrodes. When an electric voltage is applied, an electric field is created with lines running through the ceramic perpendicular to the plates. This causes a staggered contraction of the ceramic at 90° to the field lines so that the actuator constricts evenly along the plane. This behavior is called the transverse piezoelectric (d31) effect.

In the DuraAct Power patch transducer the multi-layer piezo element draws on the longitudinal or d33 effect. The displacement occurs parallel to the electric field E and the polarization direction P of the piezo actuator. The piezoelectric charge coefficients d33 for the longitudinal displacement are considerably higher than for the transversal displacement, meaning that the possible displacements are greater than for all-ceramic transducers.

The occurrence of acoustic surface waves can be converted using DuraAct Shear patch transducers. The shearing motion of the patch transducer is produced by the orthogonal application of an electric field E to the direction of the polarization P. The shear deformation coefficients d15 are generally the largest of the piezoelectric coefficients. When controlled with nominal voltages, the piezo ceramics achieve d15 (GS) values of up to 2000 pm/V. The permissible control field strength is limited in order to prevent a reversal of the vertically oriented polarization.

The electric field strength of the DuraAct patch transducers determines the displacement of the ceramic, therefore, allowing the simple control of the modules. This deformation is transmitted effectively to the structural elements via an uncomplicated bonding. The force is transmitted across the entire surface of the actuator by thrust and not at discrete points as is the case with conventional actuators. Massive force transfer points are therefore unnecessary. Conversely, structural deformations are converted to an electrical charge by the transducer, making it possible to use the element as a sensor or power generator. Division of the sensor and actuator functionality is achieved using an isolated contacting of several layers.

The reaction to a change in the electrical field or a deformation is extremely fast. This allows oscillations to be generated into the kilohertz range or also measured. Depending on the active piezo element used and its dimensions, different actuators produce different values with respect to control voltage and contraction. The relationship between deformation and control voltage is not linear.

DuraAct Patch Transducer Performance Graph

The actuator characteristics of piezoceramic transducers are primarily described by means of two parameters: the blocking force FB and the free displacement S0. If the unimpeded (free) actuator is controlled with a voltage U, it reaches its maximum displacement S0. The force required to push the maximally displaced actuator back to its original length is called the blocking force FBI.

If both parameters are plotted on a graph and connected with a line, the result is the performance graph of the actuator. The connecting line is called the load line. The ratio of external force to displacement can be read from the graph. In most applications, the actuator works against an elastic structure such as when deforming a spring or bending a plate. If the actuator deforms a spring, for example, the characteristic curve of the spring is plotted on the performance graph with the stiffness cF. The intersection point of the load lines and the characteristic curve denotes the operating point. The actuator works most effectively when the operating point is in the middle of the load lines.

DuraActアクチュエータは一般に基板に接着されており、収縮を数箇所の取付点だけでなく、面全体に伝達します。こうした構成では、DuraActと基板の組み合わせはベンディングアクチュエータとして動作します。ベンディングアクチュエータは再現性をもって迅速、高精度に変位を起こすことができ、プリンター、バルブ、繊維業界など幅広い用途に使用されています。

DuraActパッチトランスデューサーは横方向ピエゾ効果に基づいているため、電界を印加すると収縮します。このベンディングアクチュエータは図に示すように屈曲し、垂直抗力を発揮します。

自由で制止されていない曲がり素子の自由変位はW0で表します。変位を0に抑えるのに必要な力は、曲がり素子の発生力FBWと呼ばれます。この力は、アクチュエータの発生力より非常に小さくなります。これらの2点を通る曲線から、基板の厚さと弾性に対する曲がり素子の特性曲線が得られます。

図に、さまざまな素材の50 mm厚の基板サンプルとP-876 A15 DuraActパッチトランスデューサーを使用して測定した実際の変位と力を示します。

曲がり素子の特性曲線は、DuraAct単体の特性曲線と組み合わせることで、効率良く特定の用途におけるアクチュエータの性能を推定できる基準となります。このため、弊社では、すべてのデータシートにこれらの曲線を記載しています。

ベンディングアクチュエータのパラメーター

DuraAct Patch Transducer Power Requirements

To estimate the electrical requirements necessary for the operation of an actuator, the capacitance of the transducer plays an important role. The capacitance values of DuraAct patch transducers are typically in the nanofarad range and in each case are provided on the datasheets.

Here, the capacitance C is dependent on the type, thickness and area of the piezo ceramic used. To estimate the average electrical output Pm, the control frequency as well as the capacitance of the transducer and the voltage swing are required.
 

Pm = C · f · Uh2

f: frequency, Uh: voltage swing
 

The maximum power requirement Pmax can be calculated by multiplying the average electrical output by pi (π):
 

Pmax = Pm ・ π

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パンフレット

DuraAct Piezoelectric Patch Transducer

Flexible, Efficient, Durable
日付 / バージョン
BRO07E R1 2019-06
日付 / バージョン
BRO07D R1 2019-06
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