DD226363A1 - EXPANSION TRANSFORMER - Google Patents

Abstract

The invention relates to a strain transformer for the transmission of surface voltages in electrical signals and is used in the fields of technology, where processes of measurement and control control z. B. for load distribution, level measurements o. Ae. to be recorded. According to the invention, two plate-shaped materials with different elasticity modules and geometric dimensions are connected to one another in such a way that the characteristic curve of the transfer function can be varied with regard to linearity and increase. Targeted nonlinearities, for example for switching elements, can be realized by rotation of the substrate from the trivial stress direction. The substrates carrying the transducer can be produced by microelectronic production methods (mass production). An advantageous embodiment of the invention is to provide the carrier substrate and / or the transducer for improving the thermal conductivity with one or more electrically conductive and non-conductive layers. Fig. 1

Description

Title of the Invention Strain Transformer

Field of application of the invention

The invention includes an expansion transformer, which is used as an autonomous measuring device for converting mechanical Verforraungszustände into electrical signals. These devices, generally referred to as strain gauges, generate electrical signals proportional to the surface tension of the measurement object for further information processing. The use of stretch transformers can be used in many fields of technology with process measuring, control and monitoring systems, eg. in transport, handling and storage processes, in construction, the light and food industry or robotics.

Characteristic of the known technical solutions

Means for detecting mechanical deformation states are known in the form of so-called expansion elements. Strain gauges and strain transformers are used to increase the measuring effect.

In US 2218909 an apparatus for detecting and amplifying mechanical stresses is described which exploited the elongation magnification in a gap, which is filled with a relatively soft filler.

DE 2902242 presents a solderable strain gauge which is sputtered onto a temperature-resistant plastic support having a diametrically disposed solderable layer. DE 2 606 753 and DE 2 901 995 describe expansion transformers which determine mechanical deformation states by fixing them parallel to the measurement surface. Disadvantages of the solutions mentioned are the known large creep rates of the plastics used, the relatively high technological expenses for the production of the deformation body and despite high technological cost only limited opportunities for the targeted influencing the Obertragungskennlinie, eg to avoid or intentional generation of non-linearities.

Object of the invention

The aim of the invention is to transform a strain transformer, the mechanical deformations into electrical signals, taking advantage of the elongation magnification influencing the Obertragungskennlinie possible is economical to manufacture and which is universally applicable to develop.

Explanation of the essence of the invention

It is an object of the invention to provide an expansion transformer, which combines the advantages of the expansion, in particular for detecting small mechanical stresses and deformation states with a simple applicability by the user.

According to the invention the object is achieved in that two plate-shaped materials with different moduli of elasticity (Ε-module) are firmly connected to each other »wherein the deformation body with the larger Ε-module E _{1 of} the coupling with the DUT serves and the carrier substrate with the smaller modulus of elasticity E ₂ carries the electrical converter. Assuming the solid preferred combination of both materials with E ₁ and E _p :

E ₁ (y = h ₁ -e) = £ ₂ (y = h ₁ -e) / la /

U (y = H ₁ -e) = S ^ (y = H ₁ -e) / Ib /

⁴² I ^W 2

It follows the relationship of the constants C ^ ₂ = C _1/2 /

Assuming the equivalence of the shape change above and below the neutral fiber e, without additional longitudinal force, results

h "- e h _± + h ₂ - e

dy + / ~ 0 ₂ dy = 0

- eh ₁ - e

and from this the position of the neutral fiber

9 O P

h, + - = (h, + -2h, h _p )

e = 1-g / 4 /

2 (H ₁₊ ^ Sh ₂ )

It is evident that the neutral axis e can be displaced significantly by variations of the Dicks h ^ of the carrier substrate, which is of direct influence on the strain S at the upper side of the deformable body or £ in the transducer on the top surface of the substrate. While the measurement information registered in the transducer represents ζ, the surface strain of the deformation body to be transmitted to the carrier substrate is ζ . The transfer of £ is responsible in its absolute value for the shear stresses occurring in the coupling layer. From the above relationships can therefore be determined by a suitable choice of the ratio h. to h _2, the shear stress in the coupling layer can be chosen so that with knowledge of the elastic properties of the coupling layer, an overstretching is prevented in this. This minimizes hysteresis and reproducibility errors and improves the stability and accuracy of the strain transformer. For the support substrate such materials as glass, glass ceramic, ceramic or the like are available, the selection of which is easily possible from the later application requirements and the knowledge of the elastic parameters of these materials. In such a VVandleranordnung the carrier substrate with the smaller

Elastic modulus E ₂ advantageously formed as a finite limited substrate. This has the advantage of economical production of complete, robust expansion substrates according to production methods of microelectronics production. In addition, the vaulting processes occurring at the corners and edges of the substrate plate can be used specifically for further influencing the transfer characteristic. As a result, elongation effects beyond the previously discussed strain exaggeration by different modulus of elasticity module can be achieved. In this way, characteristic curves of the transfer function can be purposefully influenced, as can be desired in switching elements z.3.

The erfindungsgeraäße effect of the characteristic influencing can also be used for shear stress sensors in which also by utilizing edge stress effects, the distribution of the surface strain, here due to the shear stress and superimposed bending stresses, by local distribution of the strain-sensitive zones and the layer thickness ratio of substrate and deformation body are influenced according to the Anvvendungszwecken can.

For the transducer material sputtered or vapor-deposited metal layers can be used. However, for medium and higher application requirements, preference is given to metal foils which are adjusted to a specific temperature dependence of the specific resistance by a series of complicated temperature treatments and have a high long-term stability. The temperature dependence of the resistivity of the metal foils or other electrical metal layers is chosen according to known physico-mathematical contexts that virtually no temperature dependence of Dehnnungstransformator.s detectable later use on the object to be measured. In this context, it has proven to be beneficial to provide special measures for heat conduction. It is found that directly after application of the supply voltage occurring thermoelectric voltages and initial stresses due to heat loss power in the carrier substrate by one or more thermally conductive intermediate layers, applied to the carrier substrate or on one or both sides of the transducer minimized

and the strain transformer thereby has an improved transient behavior. Metallic layers which are protected, for example, by additional electrically insulating layers, for example SiO ₂ , can also be used as the heat-conducting intermediate layers.

embodiment

The invention will be explained in more detail with reference to drawings and a calculated example.

FIG. 1: Scirematic representation of the expansion transformer FIG. 2: Diagram

Fig. 3: strain transformer with intermediate layers for heat dissipation

Fig. 4: Schematic representation of a mounted expansion transformer

As shown in Fig. 1, the strain transformer consists of a deformation body 1 with the Ε-modulus E ^, the thickness h * and the width b ,, on the means of an adhesive layer 4, the support substrate 2 with the Ε-module E ₂ , the Thickness h ₂ and the width b ~ is applied. By suitable technical measures (sticking, sputtering, vaporizing, etc.), the transducer 3 is fastened on the carrier substrate 2.

The deformation body 1 is made of a steel alloy with E. = 210 GPa and have the dimensions b _± = 20 mm and h. = 1.4 mm.

The carrier substrate 2 is made of a glass ceramic with E ₂ = 50 GPa and have the dimensions b "= ₈ mm and h ₉ = 0.7 mm. Taking into account a permissible elongation C = 1. 10 in the converter 3 are to be continuously evaluated bending moments of a load component in the range 0 to 600 Nmm. In the case of direct application of the transducer 3 to the deformation body 1, an elongation _{Q Q} is determined at a maximum bending momentum M = 600 Nmm. «F ^ after

from 0.44. 10 "in the converter 3 effective.

Due to the additional use of the carrier substrate 2, the position of the neutral fiber is shifted according to the relationship 4 to e = 0, Sl mm. The resulting elongation £ at the upper

side of the deformation body 1 is calculated

H. - e

where I _{0 is} the total area moment of inertia with ¹ G =

represents.

For the maximum bending energy M = 500 Nmm, an elongation of only ε = 0.35 * 10 thus becomes effective on the surface of the deformation body 1.

The support substrate 2 is made of a glass ceramic with E ₂ = 50 GPa and have the dimensions length times width b "· b" = (25 χ 25) mm and thickness h ^ 0.7 mm.

The course of the neutral fiber reaches the value e according to the relationship / 4 / for localized carrier substrates by loss effects only in the center of the substrate plate, (see Fig. La). Accordingly, at the edges of the substrate plate, the coefficient of transfer of the longitudinal expansion drops, but in accordance with FIG. 1b the rotation in the correspondingly marked areas increases. For the described layer thicknesses, moduli of elasticity and dimension combinations, elongation increases to about 150 % compared to applications which take place directly on the deformation element and without a glass-ceramic substrate. Likewise, by varying the layer thickness ratio, the linearity errors can be varied in a problem-oriented manner. For

the example described h / h = 0.24 becomes the linearity error 6 ^ _n = 2. 10 ~ ³ .

On the other hand, non-linearities can be deliberately generated in the transducer 3 of strain transformers with substrates rotated from the original (arivial) stress direction. The characteristic curve of the converter output voltage U _Q for a 45 ° -oriented substrate is shown in FIG. The characteristic curve can be advantageously used for switching effects or tara compensation on level measuring systems.

Analogous to FIG. 1, the expansion transformer shown schematically in FIG. 3 consists of the deformation body 1, a carrier substrate 2 and a transducer 3. On the transducer 3, intermediate layers 31 are formed on both sides of the transducer 3 for better heat conduction.

introduced. This can be technically e.g. be solved, which are first applied to the metal foil by a suitable method SiOp as electrical insulation layer 31 a and then a metallic layer 31 b and provided after completion of the composite system transducer 3 carrier substrate 2 in reverse order with electrical insulation layer 31a and metallic layer 31 b become. 4 shows schematically a completed expansion transformer. The preassembled deformation body 1 with carrier substrate 2 and transducer 3 receives a cover 32 * The transducer is electrically connected by thin contact wires 33 with glued soldering pads 34. The connecting wire 35 is guided via a strain relief 35 to the outside. The holes 5 in the deformation body 1 are used for attachment to the load component.

Claims (1)

claim An expansion transformer for transmitting mechanical deformation states into electrical signals, characterized in that a deformation body having a modulus of elasticity E ₁ and a thickness h 1 having a support substrate having the modulus of elasticity Ep and the thickness h~ is a transducer according to the relationship ^ ^{2 h} l * ⁺ E ^ ^ ^h 2 ^{2 + 2 h} l ^h 2 ⁾ be connected, in the converter, a strain increase c- and in the coupling layer between the deformation body and the carrier substrate a strain reduction is realized £. Elongation transformer according to claim I _1, characterized in that the transmission characteristic is influenced by the expansion superelevation δ . Elongation transformer according to Claim 1, characterized in that linearity profiles are determined by planimetrically rotated substrates in their orientation direction, preferably by 45 °. Elongation transformer according to claim I _1, characterized in that the carrier substrate and / or the converter receive one or both sides thermally conductive and electrically insulating layers.