WO1996041384A1

WO1996041384A1 - Piezoelectric bending transducer

Info

Publication number: WO1996041384A1
Application number: PCT/DE1996/000996
Authority: WO
Inventors: Christian Stein; Thomas MÖCKL; Michael Riedel
Original assignee: Siemens Aktiengesellschaft
Priority date: 1995-06-07
Filing date: 1996-06-05
Publication date: 1996-12-19
Also published as: DE19520796A1

Abstract

The object of the invention is to provide a piezoelectric bending transducer in which inherent bending brought about by heat is prevented when the transducer is subjected to thermal stress. According to the invention, this object is achieved in that the bending transducer (2, 12, 14) has a piezoceramic layer (6, 8) applied to a carrier layer (4, 16, 18) and the materials of the piezoceramic layer (6, 8) and of the carrier layer (4, 16, 18) have substantially identical coefficients of thermal expansion.

Description

Be honored

Piezoelectric bending transducer

The invention relates to a piezoelectric bending transducer with a piezoceramic layer which is applied to a carrier layer.

Piezoelectric bending transducers are used, for example, to guide yarn in looms, in braille readers and in video devices. The structure of a piezoelectric bending transducer is described for example in WO 92/02961 AI. The bending transducer described there comprises a carrier layer in the form of a graphite fiber layer, which is provided between two electrodes provided on both sides

Piezoceramic layers are glued with an epoxy resin. The graphite fiber layer has a greater length than the two piezoceramic layers. A copper foil is glued to the free part of the graphite fiber layer, and on this copper foil is a surface for attaching a

Solder contact provided. In this way, contacting the inside, i.e. electrodes lying between graphite fiber and piezoceramic layer are comparatively simple. Instead of the graphite fiber layer, it is known to use metallic materials as the carrier layer.

From DE-A 35 18 055 a piezoelectric actuation device is also known, in which a relaxation layer is inserted between two piezoelectric ceramic layers to reduce stresses.

Basically, there is the problem with a piezoelectric bending transducer described at the outset that under the action of temperature it shows its own bending, which interferes with its function, because it occurs in a

Variety of applications not to drift the zero point position depending on the temperature of the bending transducer.

The invention is therefore based on the object of specifying a piezoelectric bending transducer which has only extremely little or no inherent bending under the influence of temperature.

This object is achieved according to the invention in a piezoelectric bending transducer with a piezoceramic layer which is applied to a carrier layer in that the material of the piezoceramic layer and the material of the carrier layer have essentially identical thermal expansion coefficients. The carrier layer serves on the one hand to stabilize the bending transducer and on the other hand guarantees reliable transmission of a mechanical bending of the bending transducer to a control element or to another part of the device to be moved in which the bending transducer is used.

Advantageously, the material of the piezoceramic layer is a lead zirconate titanate ceramic (PZT ceramic), the material of the carrier layer having a coefficient of thermal expansion of 2 × 10 ^"ε to 8 x 10" ⁶ per Kelvin, preferably 3 5 x 10 ^"s to 5.5 x 10" ⁶ per Kelvin. In this way, the thermal expansion coefficient of the carrier layer is particularly good at the thermal expansion coefficient of the polarized lead-zirconate-titanate ceramic, which usually has a thermal expansion coefficient of 3 x 10 ^"s to 7 x 10 ^{~ 6} per Kelvin The polarization serves to develop the piezoelectric effect. Thickness tolerances of the carrier layer or the piezoceramic layer with regard to the thermal inherent bending of the bending transducer are then of minor importance. The bending transducer is particularly suitable as a single-layer bending transducer, as a so-called Unimorph bender. In a particularly advantageous embodiment, the material of the carrier layer can be silicon, glass or an oxide ceramic, preferably zirconium oxide or aluminum oxide. The materials mentioned are inexpensive and easy to handle in terms of production technology. The PZT ceramic of the piezoceramic layer can also be selected as the oxide ceramic.

The contacting of the carrier layer and / or the side of the piezoceramic layer facing the carrier layer is achieved in a particularly simple manner by a corresponding metallization layer. Such

Metallization layers can be applied in a particularly advantageous manner by sputtering technology.

Furthermore, it can be provided that a piezoceramic layer is arranged on each side of the carrier layer, as is the case, for example, in the case of a bending transducer for a braille reading device.

Particularly when the carrier layer is an electrically non-conductive layer, e.g. B. a carrier layer made of glass or oxide ceramic, contacting of the piezoceramic layers arranged on both sides is provided in a particularly advantageous manner by means of a contact placed around an edge of the carrier layer or through a bore in the carrier layer. In this way, both metallization layers facing the carrier layer have the same electrical potential. Likewise, however, in the case of an electrically non-conductive carrier layer, the two electrodes located on the inside can also be set to different potentials, so that the bending transducer can also be actuated with an antiparallel polarization direction of the two piezo-ceramic layers.

Embodiments of the invention are explained in more detail with reference to a drawing. Show: IG 1 in perspective schematic representation of the structure of a piezoelectric bending transducer; IG 2 a first embodiment for contacting piezoceramic layers applied on both sides; and IG 3 a second embodiment for contacting piezoceramic layers applied on both sides to one another.

The same parts have the same reference numerals in FIGS. 1 to 3.

1 shows a carrier layer 4 and two piezoceramic layers 6, 8, which are connected to the carrier layer 4 in the form of two piezoplates 6, 8. The piezo plates 6, 8 have a thin metallization layer 10 on the side facing the carrier layer 4. The carrier layer 4 consists of an approximately 200 μm thick silicon layer. The material of the carrier layer has a coefficient of thermal expansion of about 5 x 10 ^{~ 6} per Kelvin. This coefficient of thermal expansion thus largely corresponds to the coefficient of thermal expansion of the material of the piezo plates 6, 8. The piezo plates 6, 8 made of a lead zirconate titanate ceramic (PZT layer). The piezoplates 6, 8 have a thickness of approximately 100 μm and each have a metallization layer 10 applied on the side facing the carrier layer 4 using sputtering technology.

Because the expansion coefficients of the carrier layer 4 and the piezo plate 6, 8 are largely matched to one another, the piezoelectric bending transducer 2 shows only a negligible thermal inherent bending under the influence of temperature. The piezoelectric bending transducer 2 is therefore suitable half very particularly for applications in which an exact zero point adjustment over a wide temperature range is important, for example from -20 ° C. to +80 ° C.

Figures 2 and 3 each show a side view

Excerpts of bending transducers 12, 14, which are constructed in principle like the piezoelectric bending transducer 2 in Figure 1. The piezoelectric bending transducer 12 differs from the bending transducer 2 in that a carrier layer 16 made of glass is provided. In order to pull the piezoplates 6, 8 to the same electrical potential, the carrier layer 16 has a metallization layer 10 in a manner similar to the piezoceramic layers 6. This metallization layer 10 is designed as a contact placed around the edge of the carrier layer 16.

In the exemplary embodiment according to FIG. 3, the piezoelectric bending transducer 14 has a carrier layer 18 which consists of an oxide ceramic, here zirconium oxide. The carrier layer 18 could equally well consist of aluminum oxide. Because zirconium oxide, as well as glass, and also aluminum oxide are insulators, in the exemplary embodiment according to FIG. 3, a bore 20 is provided in the carrier layer 18, which likewise has the metallization layer 10 on the inner walls. In this way it is also ensured in the case of the piezoelectric bending transducer 14 that the piezo plates have the same electrical potential on their side facing the carrier layer 18.

As with the carrier layer 4 is with the

Carrier layers 16, 18 each achieve an adaptation to the thermal expansion coefficient of the corresponding piezoceramic layer 6, 8. In this way, the thermal inherent bending occurring in the piezoelectric bending transducers 12, 14 is also negligible in a wide temperature range. The invention is in principle applicable to all bending transducers, in particular for use in jacquard or rustling machines or braille readers.

Claims

claims

1. Piezoelectric bending transducer (2, 12, 14) with a piezoceramic layer (6, 8), which is applied to a carrier layer (4, 16, 18), characterized in that the material of the piezoceramic layer (6, 8) and that Material of the carrier layer (4, 16, 18) have essentially identical coefficients of thermal expansion.

2. Piezoelectric bending transducer (2, 12, 14) according to claim

1, characterized in that the material of the piezoceramic layer (6, 8) is a lead zirconate titanate ceramic and the material of the carrier layer (4, 16, 18) has a coefficient of thermal expansion of 2 x 10 ^{~ 6} K ^-1 to 8 x 10 ^{~ 6} K " ¹ , preferably from 3.5 K ^{" 1} to 5.5 x 10 ^"6 K ^{" 1} .

3. Piezoelectric bending transducer (2) according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the material of the carrier layer (4) is silicon.

4. Piezoelectric bending transducer (12) according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the material of the carrier layer (16) is glass.

5. Piezoelectric bending transducer (14) according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the material of the carrier layer (18) is an oxide ceramic.

6. Piezoelectric bending transducer (14) according to claim 5, characterized in that the material of the carrier layer (18) is zirconium oxide or aluminum oxide.

7. Piezoelectric bending transducer (2, 12, 14) according to one of claims 1 to 6, characterized in that the carrier layer (4, 16, 18) and / or the side of the piezoceramic layer facing the carrier layer (4, 16, 18) (6, 8) has a metallization layer (10).

8. Piezoelectric bending transducer (4, 12, 14) according to one of claims 1 to 7, d a d u r c h g e k e n n z e i c h n e t that a corresponding piezo ceramic layer (6, 8) is arranged on each side of the carrier layer (4, 16, 18).

9. Piezoelectric bending transducer (4, 12, 14) according to claim 8, characterized in that a contact of the piezoceramic layers (6, 8) with one another by means of an edge of the carrier layer (4, 16, 18) or through a bore (20th ) in the carrier layer (4, 16, 18) placed contact (10) is provided.