Patent Grant
8222797
This application is a U.S. National Stage Application of International Application No. PCT/EP2008/061180 filed Aug. 27, 2008, which designates the United States of America, and claims priority to German Application No. 10 2007 043 263.3 filed Sep. 11, 2007, the contents of which are hereby incorporated by reference in their entirety.
The invention relates to an information converter which comprises at least two material layers having polygonal base surfaces, which are connected to each other in a shear-rigid way, and wherein at least in one material layer a change of length can be induced. Such information converters are used in automation engineering either as sensors or as actuators.
From the prior art it is known for at least two material layers with different expansion behaviors to be connected to each other in a shear-rigid way to form a composite material. The expansion behavior can be influenced piezoelectrically, magnetostrictively, electrostrictively, thermally or by means of shape memory alloys. The different expansions of the two material layers then causes a bending of the composite material, which can be induced electrically or thermally. The external shape of such a composite material according to the prior art is always cuboid, the boundary surface between the two material layers always running parallel to the plane of maximum expansion. The line of intersection of the two materials consequently runs inside the narrow side. The base surface in the plane of maximum expansion of the cuboid is always rectangular or square.
In order to make the relative bending of the composite material usable as an information converter, a narrow side is usually clamped in a holder. This then defines the zero point of movement.
In an actuator, the movement of the strip on the narrow side opposite the holder can then be picked up. In a sensor, an electrical signal can be generated from the movement of the narrow side opposite the holder, or a thermal loading is converted into a mechanical movement.
In order to increase the mechanical output or work capacity of an actuator, it is known from the prior art for a plurality of material layers to be connected to each other in a shear-rigid way. Care should be taken here to ensure that the respective deformations of the strips do not cancel one another out but add to one another. In this way, the force available is multiplied.
Taking this prior art as its starting point, according to various embodiments the work capacity and/or the operational stability of a known information converter can be improved.
According to an embodiment, an information processor may comprise at least two material layers having polygonal base surfaces, which are connected to each other in a shear-rigid way, and wherein at least in one material layer a change of length can be induced, characterized in that the polygonal base surface has at least two different interior angles.
According to a further embodiment, the polygonal base surface may comprise at least one approximately right interior angle. According to a further embodiment, the polygonal base surface may comprise at least one interior angle of from about 35° to about 85°. According to a further embodiment, the polygonal base surface may comprise at least one interior angle of from about 55° to about 80°. According to a further embodiment, the polygonal base surface may have 3 or 4 vertices. According to a further embodiment, the polygonal base surface may have 3 vertices. According to a further embodiment, the cross section of the at least 2 material layers may decrease along the maximum extension of the polygonal base surface. According to a further embodiment, a mechanical holder may be provided in the region of the maximum cross section of the at least 2 material layers. According to a further embodiment, at least one material layer may contain a material which exhibits a piezoelectric effect. According to a further embodiment, a device can be provided with which an electric field can be generated inside the piezoelectric material parallel or anti-parallel to the direction of polarization. According to a further embodiment, the direction of polarization of the piezoelectric material may stand essentially vertically on the boundary surface of the at least two material layers. According to a further embodiment, the piezoelectric material may contain at least one lead zirconate titanate and/or one lead magnesium niobate. According to a further embodiment, the information processor may comprises a bending actuator. According to a further embodiment, the information processor may comprise a sensor. According to a further embodiment, the information processor may be a temperature sensor. According to a further embodiment, the information processor may be an acceleration sensor.
According to another embodiment, in a method for the production of an information processor, at least 2 material layers are connected to each other in a shear-rigid way to form a semi-finished product, wherein at least in one material layer a change of length can be induced, and subsequent separation of information processors from the semi-finished product along predetermined breaking edges, characterized in that first predetermined breaking edges are introduced essentially at right angles to the outside edges of the semi-finished product, and second predetermined breaking edges have an angle of from about 35° to about 85° relative to the first predetermined breaking edges.
According to a further embodiment of the method, third predetermined breaking edges can be provided essentially at right angles to the first predetermined breaking edges, and the second predetermined breaking edges run through the points of intersection of the first and third predetermined breaking edges. According to a further embodiment of the method, third predetermined breaking edges can be provided which have an angle of from about −35° to about −85° relative to the first predetermined breaking edges, and the points of intersection of the second and third predetermined breaking edges come to lie essentially on the first predetermined breaking edges. According to a further embodiment of the method, the angle between the third and first predetermined breaking edges may correspond to the negative of the angle between the second and first predetermined breaking edges. According to a further embodiment of the method, the second predetermined breaking edges may have an angle of from about 55° to about 80° relative to the first predetermined breaking edges. According to a further embodiment of the method, the at least 2 material layers can be connected to each other in a shear-rigid way by means of bonding. According to a further embodiment of the method, the at least 2 material layers can be sintered to each other in a shear-rigid way.
According to yet another embodiment, a pointer instrument may comprise a bending actuator as described above.
The invention will be illustrated in greater detail below with the aid of drawings and examples, without limiting the scope of the general inventive idea.
According to various embodiments, an information converter comprises at least two material layers having polygonal base surfaces, which are connected to each other in a shear-rigid way, and wherein at least in one material layer a change of length can be induced, the polygonal base surface having at least two different interior angles.
The information converter according to various embodiments has at least two material layers which are connected to each other in a shear-rigid way. This connection can be achieved, for example, by bonding, sintering or welding. Of the at least two material layers at least one must exhibit a change of length which can be induced externally by an applied signal. This signal can, for example, be an electric field, a magnetic field or a temperature change.
If only one material layer exhibits an inducible change of length, this is mounted in a shear-rigid way on a carrier material which exhibits a smaller change of length or no change of length. However, it is of course also possible for a plurality of material layers having an inducible change of length to be joined such that the mechanical stresses in the material add to one another and the bending is thereby increased. For example, two material layers having an inducible change of length can be mounted in this way on either side of a passive substrate. Alternatively, 2, 4 or 6 material layers having an inducible change of length can be mounted on one another directly without a passive carrier.
In order to make the relative bending of the at least two material layers usable for an absolution change of position, a holder is also provided in the case of the information converter according to the various embodiments, in which holder one side of the information converter is clamped. The information converter thus comprises a bending beam clamped on one side.
According to various embodiments, it was now recognized that at the point at which the maximum mechanical loading occurs, i.e. directly at the clamp, the mechanical stress can be reduced if the information converter does not have a cuboid shape with a rectangular base surface but has the shape of a prism. For the purposes of the various embodiments, the area of the free bending beam is viewed as the base surface. The area inside the clamp is largely left to the person skilled in the art.
The base surface of the prism is characterized in that it has at least two different interior angles. An interior angle of the base surface is the term that designates an angle enclosed by two sides, which lies inside the base surface. An interior angle always lies at a corner of the base surface. In the case of the base surface of a cuboid, all the interior angles are always 90°. Consequently, there is only one different interior angle. The base surface of the prism shape according to various embodiments, by comparison, has at least two different interior angles.
In one embodiment of the information converter, the base surface is chosen in the shape of an equilateral triangle. It was possible to show for a symmetrically structured bimorph bender, i.e. a composite of two identical material layers the deformation of which is added together, that, given equal deflection of the vertex, the mechanical stress at the clamping point is lower by a third than in the case of a cuboid bimorph. This is particularly advantageous where one or more material layers are composed of ceramic, since ceramic materials can accommodate only low tensile stresses. At the same time, some ceramics exhibit a strong piezoelectric effect and are therefore particularly suitable for piezoelectric information converters.
In another embodiment, the information converter has a symmetrical, quadrangular base surface in which the width at the holder is greater than the width on the side opposite to the holder. The base surface thus forms a tapering trapezium. This shape increases the load-bearing capacity of the freely swinging end of the composite material which acts as a bending beam.
If the polygonal base surface of the information converter according to various embodiments comprises at least one interior angle of approximately 90°, in one embodiment the amount of material occurring as waste in the production of the information converter can be minimized. The reasons for this are, in particular, that one information converter can be added to a further point-symmetrical information converter to form the external shape of a rectangle again.
If the interior angles are not right angles, these are chosen from the range from about 35° to about 85°, in particular from about 55° to about 80°. These ranges of angles correspond to an aspect ratio of length to width of from about 2:3 up to about 20:3. The length is measured here from the holder to the outermost freely swinging edge. The width corresponds to the line of intersection of the material layers with the mechanical clamp. The material layers preferably have a constant thickness. Since, however, in the information converters according to various embodiments, the width changes with the length, the cross section of the at least two material layers decreases along the length.
If an actuator according to various embodiments contains at least one material layer which exhibits a piezoelectric effect, it was possible to prove that, due to the basic shape according to various embodiments, the blocking force compared with the prior art is greater by a third for an actuator of the same volume. Blocking force is the term used to designate the force which is necessary to bend a fully deflected information converter back to the zero position.
The no-load deflection of unloaded actuators according to the prior art and according to the various embodiments is identical. Consequently, the quality of the actuator, i.e. the product of blocking force and deflection, is also greater by a third. In a piezoelectric bending actuator, this leads to an increased work capacity for the same consumption of piezoelectric material or to a lower consumption of material for the same work capacity. In the case of a piezoelectric sensor, an acceleration sensor for example, the electrical measurement signal is greater given the same deflection. Consequently, this gives rise to an improved signal/noise ratio and thus a greater measurement accuracy.
In order to produce a piezoelectric effect in at least one material layer, a device is provided for generating in the material an electric field parallel or anti-parallel to the polarization. This can be achieved, for example, with electrodes which are applied to the outside of the piezoelectric material layer by means of sputtering or thermal evaporation. In individual cases, an electrically conductive carrier material can also be used, to which the piezoelectric material layer is applied in a shear-rigid way.
Suitable piezoelectric materials include for example lead zirconate titanates or lead magnesium niobates or mixtures of one or more of these materials. The ceramic materials specified exhibit a particularly strong piezo effect, i.e. a particularly large change of shape as a function of the electric field. By applying the electric field anti-parallel to the polarization of the piezo material, the latter undergoes a longitudinal compression and lateral extension. When an electric field is applied parallel to the direction of polarization, the material undergoes longitudinal extension and lateral compression. Where two material layers with opposing directions of polarization are shear-rigidly connected, the composite strip thus formed undergoes amplified deformation when an electric field is applied. Of course, this amplification can also be achieved if the directions of polarization are chosen in the same direction and the electric field acts in opposing directions in each material layer.
For use as an actuator, an electric voltage is applied to the holder 2 and the conductive coating of the piezoelectric material layer 3. By this means, an electric field E appears inside the material layer 3. This electric field leads to a contraction of the length of the material layer 3. The carrier material 2 is not affected by the electric field and maintains a constant length. This leads to a mechanical stress in the information converter and subsequently to the bending thereof along the direction of the arrow 6.
The information converter according to
a shows the information converter from
The two material layers are connected to each other in a shear-rigid way and clamped in the holder 4. The voltage source 5 generates an electric field E which acts parallel to the polarization of the piezo material 3. Such a structure is termed a monomorph.
b shows a trimorph structure. In contrast to
The multimorph according to
a shows a bending transducer with a base surface in the shape of an equilateral triangle. For aspect ratios of length to width of from 2:3 to 20:3, the base has an interior angle of 53° to 84°. By means of the Bernoulli bending theory, a bimorph layer structure in a triangular embodiment is compared with a rectangular structure, of equal area and volume, according to the prior art. For this purpose, the bending transducer according to various embodiments is clamped on or near the base edge of the equilateral triangle. The movement is picked up at the opposite vertex of the triangle. The height of the triangle corresponds to the length of the rectangular information converter.
It has been shown here that the maximum possible deflection of the bimorph transducer does not depend on the geometry. This deflection is calculated as
Here, x0 designates the deflection, Eel the electric field which prevails inside the piezoelectric material layer 3, h its thickness and l the length of the rectangular information converter or the height of the triangular information converter.
For the blocking force of the rectangular converter, the following applies:
Here, FB signifies the blocking force, E the modulus of elasticity and b the width of the clamp.
Surprisingly, it could be shown that the blocking force of the triangular converter obeys the following formula:
The blocking force of the triangular converter is a third greater than that of the converter of equal volume according to the prior art.
The product of blocking force and no-load deflection designates the quality of a bending transducer. The quality consequently has the unit of an energy and thus indicates the theoretically possible work capacity of a bending actuator or the signal voltage generated in a sensor. Since the blocking force of the information converter according to various embodiments lies one third above that of the known converter, but the no-load deflection is identical in both cases, this also gives a value for the quality criterion that lies one third higher than that of the prior art.
The mechanical normal stress at the clamp, which is induced in the composite strip by bending back to the opposite extreme position, is influenced positively by the shape of the information converter according to various embodiments. Thus, the mechanical stress of an information converter according to the prior art is
By comparison, a converter according to various embodiments exhibits a mechanical stress of
The mechanical normal stress in the material of the information converter is thus reduced by ⅓ in the shape according to various embodiments. This gives greater operating stability and a longer service life until the information converter fails.
The results shown here based on a piezoceramic bending actuator apply analogously also to bi-metal actuators, magnetostrictive actuators and shape-memory actuators. The results can also be assigned to the corresponding sensors.
The information converter according to
In order to increase the mechanical load-bearing capacity at the pickup, a larger surface is provided at the end opposite the clamp in the trapezoidal information converter according to
The embodiment according to
To produce an information converter according to various embodiments, at least two material layers are preferably first connected to each other in a shear-rigid way to form a semi-finished product, a change of length being inducible at least in one material layer. The semi-finished product has a size corresponding to a plurality of ready-to-use information converters. These are then in a further method step separated from the semi-finished product. Occasionally, however, the person skilled in the art will also provide for separating individual parts of an information converter out of individual material layers and then joining these in a shear-rigid way to form a finished converter.
The separating is carried out by means of machine-separating or non-machine separating. For example, predetermined breaking points can be introduced into the material, along which points the information converters are then separated by breaking. For a bending transducer according to
A bending transducer according to various embodiments and according to
The production of an information converter according to
The third predetermined breaking edge is now introduced into the material, again at right angles to the first predetermined breaking edge, this third edge always running through the points of intersection of the first and second predetermined breaking edges. As a result, a rectangular semi-finished product can be fully separated, along the predetermined breaking edges introduced in this manner, into individual information converters without any unused waste remaining.
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| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/061180 | 8/27/2008 | WO | 00 | 6/1/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/033949 | 3/19/2009 | WO | A |
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