WO2012100770A1 - Electrical measuring device for measuring force and/or pressure - Google Patents

Abstract

The invention relates to an electrical measuring device for measuring force and/or pressure, comprising at least one measuring structure that is applied to a support surface, said structure consisting at least partially of a piezoresistive material.

Description

 Electrical measuring device for force and / or pressure measurement The invention relates to an electrical measuring device according to the preamble of claim! ,

Electrical measuring devices using sensor elements in the form of strain gauges (DMS), each having at least one measuring structure are known. The force- and / or pressure-dependent measurement signal is based on a

Changes in the electrical resistance of the respective measuring structure, the (resistance change) in stretching the strain gauge and thus the measurement structure occurs, i. at a load of the respective arranged on an upper surface or support surface of a substrate measuring structure in at least one extending in the surface side axial direction. For this purpose, the substrate consists of an elastically deformable material, preferably of a polymeric material, the hardness of which is smaller than the hardness of that used for the measuring structure

Material. A disadvantage of known measuring devices with

Strain gauges that always a certain way or movement stroke with significant size between two functional element of the measuring device in both the force measurement and the pressure measurement is required, which is not desirable in many cases for various reasons and / or not insignificant design disadvantages. The invention has for its object to overcome this drawback and a

Show measuring device that without a movement stroke, but at least without a noticeable movement stroke, i. with an extremely reduced movement stroke compared to the aforementioned known measuring devices, the measurement of forces and / or pressures, i. the generation of force and / or pressure-dependent electrical measurement signals possible. To solve this problem is a

Measuring device designed according to claim 1.

The peculiarity of the measuring device according to the invention is that it is designed so that the respective force to be measured and / or each of the pressure to be measured and / or derived therefrom forces or pressures perpendicular or

Confirmation copy | substantially perpendicular to the at least one measuring structure, ie

acting exclusively in an axial direction perpendicular or substantially perpendicular to the at least one measuring structure or the surface forming this measuring structure.

The term "substantially" in the context of the invention means maximum deviations

 + / - 5% and / or deviations in the form of changes that are insignificant for the function.

"Piezo-resistive materials" are in the context of the invention, such materials or materials with which on support surfaces electrical resistance or

Measuring structures can be produced, the electrical resistance changes depending on a force and / or pressure on the measuring structure perpendicular or substantially perpendicular to the support surface.

Further developments, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and from the figures. All are described and / or illustrated

Features alone or in any combination in principle subject of the invention, regardless of their summary in the claims or their dependency. Also, the content of the claims is made an integral part of the description.

The invention will be explained in more detail below with reference to the figures of exemplary embodiment. Show it:

Fig. 1 in a very simplified schematic sectional view of a

 Force measuring device according to the invention;

Fig. 2 in a simplified representation and in section the sensor element of

 Force measuring device of Figure 1;

 Fig. 3 in a simplified representation of a plan view of the sensor element of the figure

 2;

 Fig. 4 in a simplified schematic sectional view of a

 Pressure measuring device according to the invention;

Fig. 5 is an enlarged partial detail of the pressure measuring device of Figure 4; Fig. 6 in a very simplified schematic sectional view another

 Embodiment of the force measuring device according to the invention;

Fig. 7 in a simplified schematic sectional view of a

 Pressure measuring device according to the invention;

8 is an enlarged partial view of the pressure measuring device of Figure 7.

For ease of description, the figures indicate the axes of a Cartesian coordinate system which are oriented perpendicular to one another, namely the X-axis, Y-axis and Z-axis.

The force measuring device generally designated 1 in FIG. 1 is used to measure the force F acting between a first functional element 2 (force transducer) and a second functional element 3 (base) of the force measuring device 1 in the Z axis and to generate at least one of the same size Force F dependent, eg to the magnitude of the force F proportional electrical signal. The functional element 2 is in the illustrated embodiment, for example, a solid stamp-like element with a flat lying in the XY plane stamp surface 2.1. The functional element 3 is in the

illustrated embodiment, for example, a solid base or

Carrier element, e.g. of a metallic material, for example of steel (for example of corrosion-resistant steel or stainless steel) and has in the

illustrated embodiment on its upper side also a flat or plane arranged in an XY plane surface 3.1. Furthermore, in the illustrated embodiment, the area 3.1 is larger than the area 2.1, so that the

Functional element 3 with its surface 3.1 laterally over the functional element 2 and the surface 2.1 is away. In principle, the surface 2.1 could also be convex in at least one subregion.

Between the two functional elements 2 and 3 or between the mutually parallel surfaces 2.1 and 3.1, a sensor element 4 is arranged, which essentially consists in the illustrated embodiment of a plate-shaped substrate 5 with a measuring structure 6 on a substrate surface side. The substrate surface side and measuring structure 6 or the layer forming this measuring structure are arranged in an XY plane. The measuring structure is preferably designed as a meander-like conductor track. Others too Shapes for the measuring structure 6 are possible. With the measuring structure 6

the surface facing away from the substrate 5 against the surface 3.1 at.

Basically, for this purpose, the substrate 5 is designed in one or more layers in such a way that the measuring structure 6 is electrically separated from the functional element 3.

For the electrical separation between the measuring structure 6 and the functional element 2, in the illustrated embodiment, this is provided with an insulating layer 7 on its end face or surface 2.1 facing the sensor element 4 and resting against the measuring structure 6. Otherwise, the functional element 2 is also e.g. of a metallic material, for example of steel (for example of corrosion-resistant steel or stainless steel) or else the functional element is made entirely of an electrically insulating material.

The measuring structure 6 is provided at two mutually remote areas each with an electrical connection 8, via which the sensor element 4 and the force measuring device 1 can be connected or connected to a measuring and evaluation electronics 9, u.a. for generating a dependent on the size of the force F measurement signal. The measuring and evaluation electronics 9 is preferably at least partially part of the force-measuring device 1.

Via the insulating layer 7, the force F acts exclusively on the measuring structure 6 in the direction of the Z-axis or substantially in the direction of the Z-axis, i. in an axial direction perpendicular or substantially perpendicular to the surface of the substrate 5 having the measuring structure 6 and thus perpendicular to the XY-plane in which the measuring structure 6 extends. With the surface 2.1, the functional element 2 or the force F exerted on this functional element 2 acts e.g. as evenly as possible on the effective and between the two terminals 8 formed region of the measuring structure 6 limited in the Figure 3 with the broken line 6.1.

The materials used for the substrate 5, the measuring structure 6 and the insulating layer 7 are selected such that the material hardness and / or the modulus of elasticity of the substrate 5 as well as of the insulating layer 7 are each greater than the material hardness of the material used for the measuring structure 6 , Furthermore, at least the material for the substrate 5 is selected so that during the measurement no or in the Substantially no deformation of the substrate 5 takes place. As a material for the substrate 5 and the insulating layer 7, for example, ceramics are suitable

Different materials, such as ceramics based on alumina, aluminum nitride, carbide, etc. Other materials, including composites with appropriate hardness and with electrically insulating properties are suitable for the substrate 5 and / or the insulating layer 7.

The measuring structure 6 consists of an electrically conductive and / or piezo-resistive material, which is not permanently deformed, at least in the measuring range for which the force-measuring device 1 is designed, but is elastic. When

Piezoresistive material for the measuring structure 6 are suitable i.a. metallic

Materials, e.g. Ni, Cr, Ti, Pt, Cu and / or W and / or their alloys in Belly mixing ratio and / or their oxides and / or nitrides, also materials that are commonly used for the measurement structure of strain gauges, such as copper-nickel Alloys, for example, constantan (eg 54% Cu 45% Ni 1% Mn), nickel-chromium alloys,

For example, N icromeV (e.g., 80% Ni 20% Cr), platinum-tungsten alloys (e.g., 92% Pt 8% W) or platinum (about 100% Pt), titanium compounds, e.g. made of titanium hydride. As a piezoresistive material for the measuring structure 6 are also suitable

 Semiconductor materials, e.g. p-doped silicon (e.g., silicon doped with ppm regions) or n-doped silicon (e.g., silicon doped with phosphorous in the ppm range). The application of the measuring structure 6 on the substrate 5 is preferably carried out with the thin-film technology, e.g. by chemical (CVD) and / or physical (PVD) deposition methods and / or sputtering, wherein when using semiconductor material, for example of Si this silicon, either in the form of a thin monocrystalline layer or as a polycrystalline layer, e.g. is applied as a vapor-deposited polycrystalline layer. The layer thickness, which has the measuring structure 6 in the Z-axis direction, corresponds to the

Usually I have achieved with the thin-film technology layer thicknesses, for example, is klei ner than 40 // m, and is preferably in the range between 10 μνη and 20 μνη, The respectively desired shape of the measuring structure 6 by structuring a first surface or substantially flat applied Layer produced, for example using the masking and etching technique known in the art, or the application of the measuring structure is carried out using masks. Other methods for producing the measuring structure 6 are also possible, for example applying the measuring structure 6 or a layer forming this measuring structure by laminating or bonding a film forming the measuring structure from the piezoresistive materal to the substrate 5. Furthermore, it is also possible to use the measuring structure 6 using the thick film technology, ie by printing the measuring structure 6 on the substrate 5, for example by screen printing using a piezo resistive material containing paste and then baking the applied paste, with a layer thickness of the measuring structure 6, for example in the range between 10 // m and 100 / m.

Although the force acting on the measuring structure 6 is exclusively perpendicular to the XY plane of this measuring structure and it is due to the compared to

Measuring structure 6 much greater material hardness of the substrate 5 and the

Insulating layer 7 also comes to no stretching of the measuring structure 6, results between the two terminals 8 dependent on the force F

different electrical resistance, which is evaluated as a measured variable in the measuring and evaluation electronics 9. The dependent of the force F

Resistance change of the measuring structure 6 is achieved in the force measuring device 1 without a noticeable movement of the functional element 2 relative to the functional element 3.

The force measuring device 1 is designed for example as a force sensor, which can be used wherever forces F, especially large forces F measured or these forces corresponding measurement signals for a variety of purposes, such as monitoring, control, etc. are required. When the force measuring device 1 is designed as a force measuring sensor, the functional element 3 is provided with means for attaching the sensor, ie for fastening, for example, to machine parts or elements, etc. The sensor element 4 is accommodated in the interior of a hood or cup-like housing part 10, in the open side of which the functional element 3 has its sensor element 4 Side is introduced and which is connected at this open side tightly connected to the functional element 3, for example by welding. The hood-like housing part 10 is made of a suitable material, for example of a metallic material, such as stainless steel or aluminum, at least at its bottom 10.1 elastically deformable, on the inside lying the stamp-like

Functional element 2 is attached or formed. In the illustrated

Embodiment, the functional element 2 is completely inside the

Housing part 10 added, but it can also protrude through the bottom 10.1 to the outside.

Figures 4 and 5 show a schematic representation of a pressure sensor formed as a pressure measuring device 1 1 for measuring the pressure of a liquid and / or gaseous and / or vaporous medium. The

Pressure measuring device 1 1 includes i.a. a hood-like housing part 12, which is made of a suitable material, for example of a metallic material, e.g. Made of stainless steel or aluminum, and with such a strength that the housing part 12 at least within the measuring range of

Pressure measuring device 1 1 is dimensionally stable, i. is not deformed. The hood-like housing part 12 is closed at its open side with a closure 1, which has a connection for supplying the medium under pressure, so that in the interior of the housing part 12, a pressure measuring chamber 14 is formed. On a plane and arranged in an XY plane counter or inner surface 7.1 in the region of the bottom 12.1 of the housing part 12, the sensor element 4 is provided, in such a way that it with its measuring structure 6 against the at least in the region of the sensor element 4 is electrically non-conductive executed, ie For example, formed by the insulating layer 7 plane counter or inner surface 7.1 is applied, only with the active area 6.1 of the measuring structure 6, while the measuring structure 6 laterally of the active area 6.1 of the counter or inner surface 7.1 and also spaced from the inner surface of the bottom 12.1 is.

Through holes 15 in the bottom 12.1, the terminals 8 are led to the outside. Especially in the area of these holes 15, the measuring structure 6 is spaced from the counter or inner surface 7.1 and inner surface of the bottom 12.1. At the edge of the substrate 5, the gap between the substrate 5 and the inner surface of the bottom portion 12.1 by an annular seal 16 of a permanently elastic material tightly closed. The holes 1 5 are also used to vent the measuring structure 6 receiving and sealed by the seal 16 against the measuring space 14 space between the substrate 5 and the abutment or counter surface 7.1. The pressure P prevailing in the pressure measuring chamber 14 acts via the substrate 5 on the measuring structure 6 supported on the insulating layer 7 or on the counter or inner surface 7.1, again in the direction of the Z axis, ie in an axial direction perpendicular to those in XY Levels arranged surface sides of the substrate 5 and in an axial direction perpendicular to the XY plane of the measuring structure 6. The terminals 8 are connected to the evaluation and measuring electronics 9, which is at least partially part of the pressure measuring device 1 1 and in an additional housing, not shown the pressure measuring device 1 1 is housed, on which then external connections of the pressure measuring device 1 1 are provided. FIG. 6 shows, as a further embodiment, a force measuring device 1 a, which differs from the force measuring device 1 essentially only in that the sensor element 4 a is designed as a redundant sensor element and for this purpose two measuring structures 6, preferably two identical measuring structures 6, each on its own substrate 5 having. The substrates 5 are stacked with their measuring structures 6, in the direction of the Z-axis, ie in the direction of action of the force F following each other, so that the force F in turn perpendicular or substantially perpendicular to the plane of the respective measuring structures 6 and Level of the surface sides of the substrates 5 acts on both measuring structures. The measuring structures 6 are connected in each case via connections 8 and 8a to the evaluation and measuring electronics 9, specifically for the evaluation and / or processing of the measuring signals supplied by the measuring structures. These

Evaluation can be carried out in many different ways, for example in such a way that the output signal of the evaluation and measuring electronics 9 is generated by averaging or averaging of the signals supplied by the measuring structures 6. Preferably, the evaluation of the supplied from the measuring structures 6

Measuring signals but so that their size and / or time course in the evaluation and measuring electronics 9 compared and for deviations that are outside a predetermined tolerance, closed on a fault or a defect of the sensor element 4a or a corresponding error signal in the evaluation - And measuring electronics 9 is generated. Since the measuring structures 6 Only perpendicular or substantially perpendicular to the force F are applied and no deformation of the carrier or substrates 5 takes place, a redundant measurement in an optimal manner can be realized. Basically, by the formation of the sensor element 4a with at least two parallel or substantially parallel and in the direction of action of the force F offset from each other and simultaneously acted upon with this force F measuring structures 6 other properties for the sensor element 4a and the force measuring device 1 a reach, for example a Extension of the

Measuring range of the sensor element 4a and the force measuring device 1 a by the use of measuring structures 6, which are respectively suitable for different portions of the measuring range or formed, even with such or similar embodiment of the measuring device to achieve redundant measurements in each case one and the same measurement structure 6 is provided twice.

It is understood that the sensor element 4a with the at least two measuring structures can also be used in the pressure measuring device 1 1 instead of the local sensor element 4 with the aforementioned advantages. Figures 7 and 8 show in views similar to Figures 4 and 5 a

Pressure measuring device 1 1a, which differs from the pressure measuring device 1 1 of Figures 4 and 5 essentially only in that the measuring structure 6 is arranged on its support surface, which in turn is formed in the illustrated embodiment of de substrate 5, that the measuring structure 6 is applied directly to the present in the pressure measuring chamber 14 pressure medium or with its pressure. For this purpose, the measuring structure 6 is located on the side of the element forming the carrier surface, namely, the pressure measuring chamber 14

Substrate 5 is provided. In special cases it may be necessary to

Cover 6 by a protective layer, for example, against an electrically conductive and / or aggressive pressure medium in the pressure measuring chamber 14th

In the pressure measuring device 11a, a sensor element 4a corresponding sensor element may also be used with at least two measuring structures 6, and preferably with two in the direction of the Z-axis against each other offset and by an insulating carrier or separating layer, for example by a substrate 5 from each other separated measuring structures 6. A measuring structure is then arranged so that they directly or ggs. is applied via a protective layer with the pressure medium existing in the pressure chamber 14 or with the pressure thereof.

The invention has been described above by means of exemplary embodiments. It is understood that numerous changes and modifications are possible without thereby departing from the inventive concept underlying the invention.

Thus, it was assumed above that the respective sensor element 4 has only one single measuring structure 6. It is also possible to form the sensor element 4 with a plurality of measuring structures 6, for example also with a plurality of measuring structures 6 forming a resistance bridge, of which at least one measuring structure 6 with the force to be measured or with the pressure to be measured or with forces derived therefrom the above-described manner is applied. Furthermore, there is also the possibility of the

Insulate layer 7, provided that the stamp-like functional element 2 and / or at least the bottom portion 12.1 of the housing part 12 are made of an electrically non-conductive material and / or provided the measuring structure 6 on its side facing away from the substrate 5 with an electrically insulating layer corresponding material hardness is. It is also possible, in the force measuring device 1, the at least one measuring structure 6 directly on the counter-bearing forming

Apply functional element 3 or on the local area 3.1, provided that the functional element 3 is at least on the surface 3.1 electrically non-conductive.

Furthermore, it was assumed above that the at least one

Measuring structure 6 is provided on a flat surface side. Although this represents a particularly production-friendly solution, but it is also possible embodiments in which the measuring structure is provided curved on a curved surface. All versions but is common that the force and / or Pressure on the at least one measuring structure 6 always only in one

Axial direction Z-axis or substantially takes place in the Z-axis, which is directed perpendicular to the plane of the measuring structure 6.

Reference number list

I, 1 a force measuring device

2, 3 functional element

 2.1 area or investment or mating surface

 3.1 surface of the functional element 3

 4, 4a sensor element

 5 substrate

6 measuring structure

 7 insulating layer

 7.1 surface of the insulating layer 7 or investment or mating surface

8 connection

 9 evaluation and measuring electronics

10 cup-shaped housing part

 10.1 bottom of the housing part 10

 I I, 1 1 a pressure measuring device

12 cup-shaped housing part

12.1 bottom of the housing part 12th

13 housing part

 14 pressure measuring chamber

 15 hole

 16 gasket F force

 P pressure

 X, Y, Z spatial axes

Claims

claims Electrical measuring device for measuring force and / or pressure with at least one sensor element (4, 4a) having at least one measuring structure (6) applied to a carrier surface, which at least partially consists of a piezo-resistive material, characterized by a design of the measuring device (1, 1 1) in such a way that a force to be measured and / or a pressure to be measured and / or forces derived therefrom act exclusively on the at least one measuring structure (6) oriented perpendicularly or substantially perpendicular to the carrier surface. Electrical measuring device according to claim 1, characterized in that the force to be measured and / or the pressure to be measured and / or forces derived therefrom act as compressive forces on the at least one measuring structure (6). Electrical measuring device according to claim 1 or 2, characterized in that the at least one sensor element (4, 4a) or its at least one measuring structure (6) is arranged between the support surface, for example at least one support (5) and an element (2, 7) forming an abutment surface (2.1, 7.1) is that the investment or counter surface (2.1, 7,1) forming element (2, 7) and the at least ei ne carrier (5) made of a material whose material hardness and / or modulus of elasticity E at least equal, but is preferably greater than the material hardness of the at least one measuring structure (6) bi lable material. Electrical measuring device according to egg nem of the preceding claims, characterized in that the at least one sensor element (4, 4a) or its at least one measuring structure (6) on the support surface, for example, at least one support (5) is arranged so that the force to be measured and or the pressure to be measured and / or forces derived therefrom act directly on the measuring structure (6), and in that the element forming the carrier surface or the at least one carrier (5) consists of a material whose material hardness and / or modulus At least equal, but preferably is greater than the material hardness of the at least one measuring structure forming material. Electrical measuring device according to one of the preceding claims, characterized in that the force to be measured and / or the pressure to be measured and / or derived therefrom forces on the at least one measuring structure (6) without deformation or substantially without deformation of a support surface of the measuring structure (6 ) forming carrier (5) acts. Electrical measuring device according to one of the preceding claims, characterized in that the measuring structure is produced in thin-film technology. Electrical measuring device according to one of the preceding claims, characterized in that the measuring structure (6) of Ni, Cr, Ti, Pt, Cu and / or W and / or alloys thereof in any mixing ratio and / or their oxides and / or nitrides and / or or from one  Semiconductor material, for example, from p-doped silicon or n-doped silicon. Electrical measuring device according to one of the preceding claims, characterized in that the at least one support (5) or the abutment or mating surface (2.1, 7.1) forming element (7) at least in the region of at least one measuring structure (6) of an electrically not consist of conductive material, such as a ceramic, eg from an alumina ceramic and / or an aluminum nitride ceramic and / or a silicon nitride ceramic. 9. Electrical measuring device according to one of the preceding claims, characterized in that the at least one measuring structure (6) on a plane support surface z. B. of the carrier (5) is arranged, for example, between this support surface and also a plane investment or mating surface {2.1, 5, 7.1). Electrical measuring device according to one of the preceding claims, characterized in that the at least one measuring structure (6) on its the carrier surface and / or the carrier (5) facing and / or on its the carrier surface and / or the carrier (5) facing away electrically is not formed conductive and / or provided with an electrically non-conductive coating, preferably with a coating whose material hardness and / or modulus of elasticity is at least equal to, but preferably greater than the material hardness of the at least one measuring structure (6) forming material. 1 1. Electrical measuring device according to one of the preceding claims, characterized in that when forming the measuring device as a force measuring the at least one sensor element (4, 4a) between a first housing element (3) and on a second housing element (10) or on a provided there stamp-like element (2) trained investment or mating surface (2.1) is arranged. 12. Electrical measuring device according to one of the preceding claims, characterized in that when forming the measuring device as a pressure sensor, the at least one sensor element (4, 4a) in one  Pressure measuring chamber (14) is arranged such that at least one  Measuring structure (6) between a support (5) or a support forming this plate-shaped substrate (5) and the abutment or counter surface (7.1) is arranged, which is formed on the inner surface of the pressure measuring chamber (14) limiting housing part (12), and that the support or the substrate (5) forming said support comprises the at least one measuring structure (6) for Pressure measuring chamber (14) out covers. 13. Electrical measuring device according to claim 12, characterized in that electrical connections (8, 8a) of the at least one measuring structure (6) are guided through openings or bores (15) in the housing part (12), and in that the at least one measuring structure (6 ) in the region of the openings or bores (15) from the abutment or counter surface (7.1) and / or from an inner surface of the housing part (12) is spaced apart. Electrical measuring device according to one of the preceding claims, characterized in that when forming the measuring device as a pressure sensor, the at least one sensor element (4, 4a) in one  Pressure measuring chamber (14) is arranged such that at least one  Measuring structure (6) on a pressure measuring chamber (14) facing side of its support surface or its support (5) is arranged. 15. Electrical measuring device according to one of the preceding claims, characterized in that the sensor element (4a) has at least two independent or electrically separate measuring structures (6) which are applied to at least one support surface such that they simultaneously with the force to be measured and / or with the pressure to be measured and / or with forces derived therefrom exclusively perpendicular or substantially perpendicular to the carrier surface are acted upon. Electrical measuring arrangement according to claim 15, characterized in that the measuring structures (6) in the sensor element (4a) are provided offset from one another perpendicular or substantially perpendicular to their support surface, and at least one of the measuring structures (6) at least between two adjacent measuring structures (6). is provided electrically separated from each other carrier (5), to form a stack of the  Measuring structures (6) and the at least one carrier (5). Electrical measuring device according to claim 16, characterized in that each measuring structure (6) on a surface side of an independent carrier (5) is provided and in the stack, the measuring structures (6) and carrier (5) alternate.