AU2016292465B2 - Method and device for electrical force measurement by means of an insulating thin layer - Google Patents

Abstract

The invention relates to a device for electrically measuring a force (F) acting at least between two pressed-together metal electrodes (1) and metal electrode (3), characterised in that: the metal electrodes, made of hard metal, steel or low-resistance metal layers on ceramic, glass or plastic bodies with an electrical resistance in the region of a few milliohm to less than or equal to 10 ohm, and an average roughness depth R

Description

Device for Electrically Measuring a Force

The invention relates to a device for electrically measuring a

force built between at least two metal electrodes, wherein at

least one thin insulating film acts as a sensor element, the

electrical conductivity of which describes an unambiguous and

exactly traceable function of the acting force.

In general, the invention relates to the field of force

measurement technology, wherein a novel application variety is

achieved over the prior art by creating a simplified design of

the force sensors without deformation bodies. A configuration

feature used here is the application of at least one or more

homogeneous thin insulating films onto the planar or free-form

[5 surfaces of the mechanical force transmission elements,

whereby between the electrically insulated force transmission

elements and the metal electrodes a sensor design becomes

possible which, directly and without noteworthy deformation of

these elements, generates an electrical signal in the form of

a force-dependent change in voltage at a given current, the

signal describing the bijective, high-resolution and

continuous representation of the applied force on a direct

mechanical and electrical route.

This technology makes it possible to create sensors that have

high temperature stability, depending on the selected thin

insulating film, and a miniaturized design, which is to say in

an installation space of less than one cubic millimeter for

force measurement in the millinewton range, and furthermore in an arbitrarily large macro design in the newton to meganewton

range, wherein, depending on the measuring task, an arbitrary

geometric configuration of the mechanical force transmission

elements comprising applied thin insulating films a free selection with regard to installation space, force application direction and mechanical amplification ratios is achieved.

For example, as a result of being able to freely select the

cone slope of the inner and outer truncated cones, to the

outer cone lateral surface of which a thin insulating layer

was applied, free design selection of the measuring

sensitivity to be achieved is made possible, wherein tension

or compression sensor becomes possible, depending on the

geometric configuration. An additional degree of freedom in

the mechanical and electrical configuration of the force

sensors is the material selection, the design and the chemical

composition of the thin insulating film, or of the layer

system, applied to the force transmission elements, wherein

[5 the temperature stability and the measuring sensitivity of the

thin insulating film can be freely selected depending on the

requirements of the measuring task. Additionally, it becomes

possible to configure miniaturized and larger combinations of

multiple force sensors by way of thin insulating films in the

design of a combined sensor unit, for example so as to detect,

without interactions, the action of the force and the

direction of the force with respect to the 3 spatial

dimensions of width (x component), length (y component) and

depth (z component) in the space.

In general, the piezoresistive effect is sufficiently known

from the related art and first publications that became known

as early as 1920. The piezoresistive effect describes a change

in the electrical resistance of a material as a result of the application of a high external force or pressure. This effect

occurs in all materials that are moderately to highly

electrically conducting; however, compared to metals the

pressure sensitivity of semiconductors is several times greater. In principle, it should be noted that this pressure sensitivity based on the change in resistance due to the application of an external force can be increased in semiconductors by deliberately adapting the orientation of the monocrystal, which means the direction of flow of the electrical current, and the doping with impurity atoms in the carrier material.

The piezoresistive effect can also be observed on the example

of amorphous carbon layers having a diamond-like lattice

structure, as is described in patent DE 199 54 164 B4, wherein

it should be noted that it is not only possible to influence

the intensity of the piezoresistive effect in amorphous carbon

layers by way of a specific chemical composition and

[5 configuration of the lattice structure, but great

intensification of the piezoresistive effect is likewise

achieved with other thin films or multilayer systems, such as

aluminum-titanium-nitrite, aluminum-chromium-nitrite,

zirconium-oxide-nitrite or aluminum-chromium-nitrite-oxide,

and many others, by integrating impurity atoms or molecule

structures as grains in a nanocomposite carrier layer. This

means that the sensitivity of the change in electrical

resistance with respect to the degree of the force or pressure

mechanically applied from the outside is drastically increased

since, depending on the material combination and introduced

impurities, additional charge carriers in the form of ions

and/or electrons are released in the semiconductors as a

function of the pressure. This effect has been known since

1920; however, technical progress and continued development regarding the use and production of layer systems has yielded

novel material combinations and layer systems that, on the one

hand, can be applied to a wide variety of materials, such as

metal, ceramic, glass or plastic surfaces, and, on the other hand, have a material composition that comes very close to semiconductors with respect to the electrical properties.

Such piezoresistive layers, however, exhibit very strong temperature-dependent drift of the resistance, which as a

relative temperature-dependent change in resistance is in a

range of -0.4 percent to approximately -1.2 percent per kelvin

increase in temperature, which has likewise been described in

the related art. Such layers and structures, for example,

allow discrete electronic components and circuits to be

configured on planar carrier materials, for example glass,

such as are used in the production of modern flat screen

monitors. Surfaces thus coated are also characterized by

extreme mechanical strength exceeding that of hard metals,

[5 having compressive strength of more than 2 gigapascals and

temperature stability in the range of minus 100 degrees

Celsius up to 1200 degrees Celsius, depending on the selection

of the carrier body and the applied layer system.

DE 10 2010 024 808 Al describes a sensor design comprising a

piezoresistive thin carbon film having a structured

arrangement and measurement electronics. Only carbon (diamond

like carbon, DLC) layers are used. Such layers have very low

resistance. The piezoelectric functional layer is structured,

resulting in high manufacturing complexity for creating the

force entry surfaces. Additionally, the functional layer made

of DLC is coated with a wear protection layer, which can cause

electrical disturbance variables in the measuring system.

US 2003/0164047 Al describes a load sensor comprising a load

detecting element and a temperature compensating element,

wherein these two elements are made of the same material and

have the same dimensions.

DE 102 53 178 Al describes the use of a layer made of diamond

like carbon as a temperature sensor, which is preferably used

in areas of machines subject to tribology. Furthermore, the

option of simultaneously measuring pressure and temperature at

different locations of layer regions is mentioned.

List of Appendices

FIG. 1: shows a sectional illustration of the thin insulating

film load cell comprising a thin reference insulating

film for temperature compensation, serving as an

electrical half measuring bridge;

FIG. 2: shows a sectional illustration of the thin insulating

film load cell comprising a thin reference film for

temperature compensation for resistance measurement;

FIG. 3: shows a sectional illustration of the thin insulating

film load cell comprising a thin reference insulating

film for temperature compensation in a double design,

serving as a highly sensitive full measuring bridge;

FIG. 4: shows a sectional illustration of the thin insulating

film load cell for simultaneously detecting two force

directions F x and Fy comprising a thin reference

insulating film for temperature compensation for

electrical multi-channel resistance measurement;

FIG. 5: shows the composition and measuring circuit of an N

dimensional thin insulating film force sensor

comprising an n-fold measuring circuit having a multi-channel thin reference insulating film for temperature compensation; top - sectional illustration of a 2D insulating film sensor segment; bottom - rotational segment arrangement as an exemplary embodiment comprising n=4 times 2D sensor blocks and 4x2=8 measuring channels so as to measure the direction of the force and the magnitude thereof in a component-based manner;

Legend:

El-i and El-2: electrode pair Fy+Fx rotation angle

0°; E2-1 and E2-2: electrode pair Fy+Fx rotation angle

450;

E3-1 and E3-2: electrode pair Fy+Fx rotation angle

900;

E4-1 and E4-2: electrode pair Fy+Fx rotation angle

135°;

FIG. 6: shows a force-resistance characteristic curve of the

thin insulating film measuring cell, comprising an

uncoated hard metal electrode and a type_01 coated

hard metal electrode;

FIG. 7: shows a force-resistance characteristic curve of the

thin insulating film measuring cell, comprising an

uncoated hard metal electrode and a type_03 coated

hard metal electrode;

FIG. 8: shows a force-resistance characteristic curve of the

thin insulating film measuring cell, comprising an

uncoated hard metal electrode and a type_01 coated

hard metal electrode;

FIG. 9: shows a force-resistance characteristic curve of the

thin insulating film measuring cell, comprising two

uncoated hard metal electrodes, which is to say the resistance between the contact surfaces is in the

lower milliohm range at +/- 1 mOhm;

FIG. 10: shows a force-resistance characteristic curve of the

thin insulating film measuring cell, comprising two

uncoated hard metal electrodes, which is to say the

resistance between the contact surfaces is in the

lower milliohm range at +/- 1 mOhm;

FIG. 11: shows a force-resistance characteristic curve of the

[5 thin insulating film measuring cell, comprising two

coated hard metal electrodes having different

roughness levels [SiC_05 polished on SiC_03

unpolished]; and

FIG. 12: shows a force-resistance characteristic curve of the

thin insulating film measuring cell, comprising two

coated hard metal electrodes having different

roughness levels [SiC_05 polished on SiC_03

unpolished].

The invention relates, in general, to a device for

electrically measuring a force F, which acts at least between

two compressed metal electrodes 1 and a metal electrode 3. The

metal electrodes are made of hard metal, steel or low

resistance metal layers on ceramic, glass or plastic bodies

having electrical resistance in the range of a few milliohms

to less than or equal to ten ohms, and having a mean roughness

value Ra of less than or equal to 400 nanometers, and have

force-independent conductivity on the contact surfaces. The

force acts directly on a thin insulating film 2 or a thin

multi-layer insulating film 2 disposed between a metal

electrode 1 and a metal electrode 3 in a form-locked manner,

which is made of zinc oxide or stochastically reduced aluminum

oxide Al 2 0x, where x=2.4 to x=2.8, or silicon carbide or a DLC

(diamond-like carbon) layer, under the slightest relative

deformation in the range of smaller than or equal to 0.1h of

the metal electrode 1 and the metal electrode 3. Due to the

identical thin insulating film 2 or the thin multi-layer

insulating film 2 exhibiting exactly the same physical

behavior, a reference metal electrode 4, which is disposed

independently of the flow of the force to be measured and

fixed under the constant holding force of a fastening element

5, acts electrically on the metal electrode 3, so that this

reference resistance of the thin insulating film between the

metal electrode 3 and the metal electrode 4 is applied under a

constant pressing force for complete temperature compensation

of the measuring system as a half bridge or a full bridge, in

that a defined current of a high-precision power source 6

flows on the current path in a series connection via the metal

electrode 1 across the thin insulating film 2 to the metal

electrode 3 across the thin insulating film 2 to the metal

electrode 4, so that a force-dependent voltage 8 drops across

the thin insulating film between the metal electrode 1 and the metal electrode 3, and a reference voltage 9 drops between the metal electrode 3 and the metal electrode 4 of a thin reference insulating film 2, the voltage ratio thereof being temperature-independent, wherein the resulting bridge voltage of the measuring bridge or the directly measured voltage ratio defines a continuous, high-resolution and exactly describable and repeatable function of the acting force, regardless of the operating temperature of the device for electrically measuring a force, wherein the temperature-compensated voltage ratio or the measured bridge voltage is directly supplied to a signal processing and evaluation unit via an electrical connection, whereby an electrically decoupled and mechanically robust design of the force measuring device according to the invention is achieved. A geometry of the metal electrodes 1, 2

[5 and 3 can be freely selected in the form of planar surfaces or

free-form surfaces.

One embodiment of the device is characterized in that, during

the creation of the contact surfaces of the at least two metal

electrodes having a mean surface roughness Ra of less than or

equal to 400 nanometers, a form fit in the range of less than

4 micrometers across the entire contact surface is achieved,

whereby the electrical resistance between the contact surfaces

of the at least two or more metal electrodes 1, metal

electrodes 3 and metal electrodes 4 without thin insulating

film, which are produced, for example, from hard metal or

high-strength steel, or by way of metal injection molding, or

low-resistance metal layers on ceramic, glass or plastic

bodies having electrical resistance in the range of less than a few milliohms to less than or equal to ten ohms, regardless

of the applied force at which these metal bodies are pressed

together, remains constant within the tolerance range of

plus/minus 3 milliohms and, depending on the material used and the surface area of the contact surface, is established in the range between 20 milliohms and no more than 160 milliohms, whereby the metrological condition is created that only the thin insulating film 2 detects a force-dependent change in resistance.

One embodiment of the device is characterized in that the thin

insulating film 2 is applied to hard metal electrodes, steel

electrodes or metal layer electrodes on ceramic, glass or

plastic bodies having electrical resistance in the range of

less than a few milliohms to less than or equal to ten ohms,

so that the electrode base body of the metal electrode 1,

metal electrode 3 and metal electrode 4 has at least the same

strength as, or greater strength than, the thin insulating

[5 film 2, whereby deformation and damage of the thin insulating

film in relation to the carrier material due to pressing or

flaking is avoided, and the measuring system are not deformed

by the application of the force, or to an extremely small

degree, which is to say a relative deformation of less than

0.1o, so that the entire force measuring system operates

without displacement due to deformations of the mechanical

metal electrodes 1, the metal electrodes 3 and the metal

electrodes 4, and the application of the force on the thin

insulating film is thus converted into a direct change in

resistance, which is an unambiguous, high-resolution and

continuous function of the force.

One embodiment of the device is characterized in that the

mechanical transmission elements, serving as metal electrodes 1, metal electrodes 3 and metal electrodes 4 for passing on

the force between the outer force application site to the thin

insulating film 2 of the force measuring device and the thin

reference insulating film 2, which is disposed between the metal electrodes 3 and metal electrodes 4, are made of high strength steels or hard metals, by way of metal injection molding, ceramic or glass materials, having special high strength layers or layer systems applied, which are made of silicon carbide, DLC (diamond-like carbon), zinc oxide or stochastically reduced aluminum oxide Al 20x having an oxygen ratio of x equal to or greater than 2.4 to 2.8, whereby very high mechanical and chemical robustness, dimensional stability and freedom from wear of the elements of the measuring cell, comprising the metal electrodes 1, the metal electrodes 3 and the metal electrodes 4 and the thin insulating layer 2, is achieved, and this measuring cell withstands thermal loading of the thin insulating film 2 and the electrical contact with the electronic measurement evaluation circuit of the

[5 components (6, 7 to 17) in the vicinity of the measuring

device at a spatial distance of less than or equal to 200

millimeters, so that the measuring system is operated in the

temperature range of less than -80°C to +3000C, wherein far in

excess of one hundred thousand operating cycles do not result

in any change of the unambiguous force-resistance function of

the thin insulating film 2 or the thin multi-layer insulating

film 2.

One embodiment of the device is characterized in that the load

cell, comprising the metal electrodes 1, the metal electrodes

3 and the metal electrodes 4 and at least one thin insulating

film 2, are implemented as high-temperature applications in

the temperature range of -80°C to +11000C, and up to +12000C

in isolated cases, by using a temperature-resistant electrical connection between the thin insulating film 2 and the

electronic evaluation unit of the components (6, 7 to 17),

wherein the metallic conductor and insulator and the contact

surfaces of the connection system are temperature-resistant up to 12000C, having line lengths of greater than 20 millimeters up to 5 meters, due to the specific selection of the insulating film system 2 [SiC, Al 2 0,, ZnO].

One embodiment of the device, which is configured in a

miniaturized and compact design for electrically measuring a

force F in the millinewton to meganewton range, is

characterized in that a composition of the force measuring

system that is very robust and tolerates dynamic loads is

achieved as a result of the mechanical design of the metal

electrodes 1 the metal electrodes 3 and the metal electrodes

4, wherein the mean roughness value Ra of the metal electrode

contact surfaces 1 and the metal electrode contact surfaces 4

at a ratio of 30:1 to 2:1 are rougher compared to the mean

[5 roughness of the metal electrodes 3 of Ra equal to or less

than 200 nanometers, whereby the increase in the continuous

force-resistance characteristic curve of the measuring cell is

deliberately defined in an application-specific manner in that

a roughness ratio of 1:1 of the electrodes produces a

significantly lower increase in the force-resistance

characteristic curve compared to a higher ratio of X:1, where

X = 1.5 to 30.0, which causes a significantly steeper increase

in the force-resistance characteristic curve. Furthermore, the

metal electrode contact surface is configured as a shaped

part, wherein planar surfaces or free-form surfaces are used,

having defined surface roughness, which increases the adhesion

of the high-strength coatings on the force transmission

surfaces, whereby a strength of the thin insulating film 2 or

of the thin multi-layer insulating film 2 and of the base bodies of the metal electrode 1, the metal electrode 3 and the

metal electrode 4 the pressure load-bearing capacity of hard

metals of up to 2 gigapascals or of high-strength steels of up

to 1.2 gigapascal is achieved. Due to the selection the production method of the thin insulating film 2 in terms of the material selection and material treatment using available coating techniques, specific resistance characteristic values or working ranges of the force-dependent insulating behavior in the milliohm, ohm to several hundred kiloohm range are established, which in a smaller design having an installation space of a few cubic millimeters operate for the millinewton range, in an average size in the range up to one hundred cubic centimeters operate in the newton to kilonewton range, and in a large design below one cubic meter operate in the meganewton range.

One embodiment of the device is characterized in that the

measuring device of the elements (1, 2, 3 to 17) is

[5 electrically operated in the form of a half or full measuring

bridge by combining multiple thin insulating films 2 or thin

multi-layer insulating films 2, so that the measuring

sensitivity is increased several times over specifically by

the electrical interconnection. As a result of one or more

respective reference metal electrodes 4 per load cell, the

temperature-related resistance deviation is entirely

compensated for. Furthermore, a spatial arrangement of the one

measuring cell combination, comprising metal electrodes 1 and

metal electrodes 3, thin insulating films 2 and reference

metal electrodes 4, in the direction of the force application

to be measured, and a second spatial arrangement of the

elements (1, 2, 3 and 4) of the second measuring cell

combination in the direction of the interfering force

component, which is caused as a mechanically superimposed oscillation in the system, for example, make it possible to

operate a half or full measuring bridge as an electrical

differential connection, whereby disturbing signals can be deliberately reduced, or entirely compensated for, by parasitic mechanical oscillations.

One embodiment of the device is characterized in that the measuring device is electrically operated as a multiple series

connection of multiple measuring channels by way of one or

more half or full measuring bridges by combining multiple thin

insulating films (2.1 corresponds to channel one, and 2.2

corresponds to channel two) or thin multi-layer insulating

films (2.1, 2.2 to 2.n), the spatial or geometric arrangement

of the bridges being designed in such a way that the magnitude

and direction of the forces to be measured can be exactly and

simultaneously determined as a vector quantity for each

associated measuring channel by separately detecting the force

[5 application as vector components in the at least three spatial

dimensions of the Cartesian coordinate system, having a width

X, length-Y, and height-Z, and/or additionally in the polar

coordinate system of the rotational axis about the normal

vector of the X-Y plane, the Z axis and a further rotational

axis, which bijectively describe the angle of inclination with

respect to the X-Y plane.

One embodiment of the device is characterized in that both

simple and complex mechanical designs of the elements, these

being the metal electrodes 1, the thin insulating films 2, the

metal electrodes 3 and the reference metal electrodes 4, are

created as the electrical force measuring device, which by way

of the thin insulating films 2 are composed as a combination

of one or more electrical force measuring devices, comprising single layers (2) or multiple layers (2 or 2.n) applied to a

few shaped parts as planar or free-form surfaces, in a macro

design, which is to say in the range of greater than 10 mm, as

well as as a miniaturization in a micro design, which is to say in the sub-millimeter range, wherein multiple metal and/or ceramic and/or glass components are disposed in a force-fit or form-locked manner and detect moments as well as forces in a temperature-compensated manner, wherein, as a result of the application of high-resistance insulating layers in the megaohm range, these components are operated as metal electrodes 1, 3 and 4 in a manner that is electrically insulated with high resistance with respect to the external environment and sufficiently electrically insulated with respect to one another, and mechanically as well as electrically decoupled from one another without interactions.

One embodiment of the device is characterized in that the

establishment of the measuring sensitivity of the electrical

[5 force measuring device is defined with respect to the force

measuring range in the millinewton to meganewton range, and

that furthermore the direction of force is predefined by the

geometric configuration of the metal electrodes 1, the metal

electrodes 3 and the reference metal electrodes 4, in that

these are designed and manufactured as insertable bodies

having freely selectable ruled geometries as positive and

negative shapes, the dimensional deviation of which is smaller

than or equal to 6 micrometers at a mean roughness value of

the electrode contact surface of Ra smaller than or equal to

400 nanometers, for example as an inside truncated cone and an

outside truncated cone of lateral surfaces having the same

shape for measuring tensile or compressive forces, having the

thin insulating film 2 applied to the lateral surface, wherein

the cone angle, and thus the mechanical multiplication ratio of the compression or tension measuring cell, can be freely

selected. Furthermore, as a result of cylinder surfaces,

inserted into one another, of the outer cylinder and inner

cylinder having thin insulating films applied to the cylinder lateral surface, it is achieved that the radial tension force is detected, and thus the radial and axial force transmission capacity of shrink joints between cylindrical tensioning systems is measured directly, wherein this is linearly detected as a force acting between two bodies. In a further exemplary embodiment, it is possible, for the design freedom in terms of the configuration of this measuring system, to directly measure axial tensile or compressive forces with the aid of stepped cylinders, wherein the thin insulating film 2 of the two or more shaped parts is applied to the end face of the cylinder rings, and thus the axially acting tensile or compressive force of the pressed-on shaped parts is directly linearly detected in a linear manner, and likewise the direct measurement of torque is made possible in that, due to a

[5 planar bearing surface between the metal electrodes 1 and the

metal electrodes 3 and the interposed thin insulating film 2,

having a normal vector pointing tangentially to the direction

of rotation, of the mutually engaging, rotationally

symmetrical shaped parts, wherein the thin insulating film is

applied to a planar surface or free-form surface of a shaft,

the normal vector of which points in the direction of the

force to be measured acting on the cylinder circumference of

the two bodies as a rotation.

One embodiment of the device is characterized in that the

metal electrodes are electrically insulated from one another

by one or more thin insulating layers (2 or 2.n) and,

mechanically, they are designed as a ruled geometry or free

form geometry in such a way that at least two-channel or multi-channel simultaneous measurement of compressive and

tensile forces is possible by applying the thin insulating

film to the circumferential surface of two mutually connected

truncated cones on the outer surface of the respective inner electrode, which are mounted respect to the precisely fitting casing, which is to say with a surface roughness having a mean roughness value of less than 400 nanometers and dimensional tolerance of less than 6 micrometers, as two outer electrodes that are electrically insulated from one another as a negative shape, wherein no deformation or an extremely small relative deformation of less than 0.01% takes place of the metal electrodes 1, the metal electrodes 3 and the reference metal electrodes 4, which are made of hard metal for example, and the thin insulating film 2 on the truncated cone having a tip in the direction of the force application measures a compressive force, and the truncated cone having the tip counter to the force application measures the tensile force, and this electrical force measuring device thus simultaneously

[5 allows a force measurement in opposite force directions as

positively and negatively acting forces.

During the electrical measurement of a force by way of the

thin insulating layer 2 using the above-described device, an

electronic precision signal generator is used as the power

source 6, which operates either in the operating mode of a

regulated direct current source or furthermore in the

operating mode of an alternating current signal source, so

that clearly defined output current signals, usable as an

exact reference, in the form of sinusoidal, square wave or

triangular signals, for example, are supplied, with freely

selectable amplitudes and frequencies of the resistance

measuring circuit. Furthermore, a signal processing and

evaluation circuit is matched to the respective operating mode so that, depending on the application, electrical disturbance

variables from the surrounding environment, which is to say

strong electrical or electromagnetic fields, are deliberately

suppressed or compensated by way of signal filtering using a band pass filter or a band stop filter, having cut-off frequencies that are designed with the specific application in mind. Likewise, a reduction in the energy consumption of such a measuring system by more than 2 to 4 powers of ten is achieved in pulse/no pulse mode.

The dynamics of the thin film force measuring system,

comprising the metal electrodes 1, the thin insulating films

2, the metal electrodes 3 and the reference metal electrodes

4, or of the combination of electrical force measuring devices

by way of thin insulating films of the elements (1, 2, 3 and

4), supplies a temporal resolution in the megahertz range of

force curves that takes place exclusively as a result of the

design of the thin insulating films 2 and the thin reference

[5 films 4 as low-resistance measuring resistors in the range of

less than or equal to one hundred ohms to one ohm. In this

way, the increase in the measuring currents, and in particular

the edge steepness of the detected measuring voltage, which is

detected as a voltage drop across the thin insulating film

resistor and achieved in the lower microsecond to ten

nanosecond range. The measurement electronics is electrically

adapted to detect the voltage drops across the thin insulating

films (2 or 2n) with a resolution to no less than the three

digit microvolt range at a time delay of less than eight

hundred nanoseconds, so that the performance capability of the

entire measuring system with respect to the time response and

sensitivity is determined exclusively by this adaptation, and

thus temporal high-resolution and deformation-free force

measurement is made possible, which is carried out on bearing shells of turbines or high-voltage generators, for example.

The mechanical transmission elements for passing on the force

to the metal electrodes 1, the metal electrodes 3 and the reference metal electrodes between the outer force application site to the thin insulating film 2 are made of strong plastic materials or high-strength composite materials in the form of shaped parts, wherein the electrical force measuring system is created on the carrier material of the electrode base bodies made of plastic material or composite material of the metal electrodes (1, 3 and 4) as a result of the application of high-strength metal layers as the electrically conducting metal electrode of the elements (1, 3 and 4), the application of the thin insulating films (2 and 2.n) onto these metal electrodes (1, 3 and 4), and furthermore as a low-resistance electrical contact of these electrodes with the electronic measuring system in the resistance range of less than fifty milliohms of the elements (6, 7, to 17).

The metal electrodes 1, the metal electrodes 3 and the metal

electrodes 4 are electrically insulated from one another by a

thin insulating film 2, so that the capacitance and/or the

resistance of this electrical measuring cell, comprising the

elements (1, 2, 3 to 17), represents an unambiguous and

continuous function of the applied pressure force acting on

the measuring cell from the outside, wherein, for the purpose

of electrically measuring the force-dependent capacitance C or

the impedance Z, an electronic precision signal generator,

which operates in the operating mode of a regulated

alternating current signal source, is used as the power

source, so that clearly defined output current signals, usable

as an exact reference, in the form of sinusoidal, square wave

or triangular signals, for example, are supplied, with freely selectable amplitudes and frequencies of the capacitance or

impedance measuring circuit, and these, serving as an

oscillating circuit, provide excitation at the resonant

frequency, wherein the oscillating circuit is detuned as a result of the force acting between the metal electrodes (1, 3 and 4) due to a change in capacitance and/or impedance, and likewise the amplitude of the alternating current measuring signal drops across the capacitive-resistive resistance of the thin insulating film 2, the curve of which describes a bijective and continuous function with respect to the applied pressure force, and the electronic signal processing and evaluation circuit, by way of application-specific band stop filters or band pass filters, achieves almost complete suppression or compensation of disturbance signals as a result of parasitic mechanical oscillations or electrical fields from the surrounding environment.

The metal electrodes 1, the metal electrodes 3 and the metal

[5 electrodes 4 are electrically insulated from one another by a

thin insulating film 2, so that the impedance Z, which is to

say the inductive AC resistance or capacitive AC resistance,

of this electrical measuring cell represents an unambiguous

and continuous function of the applied pressing force acting

on the measuring cell from the outside, wherein, for the

purpose of electrically measuring the force-dependent

inductance L or capacitance C, an electronic precision signal

generator, which operates in the operating mode of a regulated

alternating current signal source, is used as the power

source, so that clearly defined output current signals, usable

as an exact reference, in the form of sinusoidal, square wave

or triangular signals, for example, are supplied, with freely

selectable amplitudes and frequencies of the capacitance or

inductance measuring circuit, and these, serving as an oscillating circuit, provide excitation at the resonant

frequency.

According to the invention, the measurement of forces is

achieved, as shown as exemplary embodiments in FIG. 1, FIG. 2

and FIG. 3, in that an insulating thin film (2) is applied

between at least two mechanical force transmission elements (1

and 3), which are designed as electrodes electrically

insulated from one another, the electrical resistance of the

thin insulating film being a clearly traceable function of the

acting force F, and furthermore a reference metal electrode

(4) is disposed in the vicinity outside the power flow, the

mounting of which fixes this electrode (4) at a constant

retaining force with respect to the source electrode (3).

In this way, a half or full measuring bridge can be created,

which fully compensates for the temperature dependence of the

[5 measuring system, whereby the resulting bridge voltage

describes a bijectively traceable function of the force

application between the electrodes (1 and 3), regardless of

the ambient temperature. For this purpose, the at least two

electrodes (1 and 3), or the shared source electrode (Eq or 3

), and the adjoining sensor electrodes (En) thereof, are

electrically connected to the power source (6), so that the

given and known current Iq of the regulated power source (6),

which is measured as a current I by way of an ammeter (7),

resulting in a voltage drop U or U n across the thin

insulating film on the multidimensional sensor, which is

measured in a high-resolution manner by way of a voltmeter (8)

and transferred as a bridge voltage with respect to one or

more reference measuring electrodes (4 or U.ref(n)) using a

half or full measuring bridge, whereby complete compensation of the temperature dependence of the thin insulating film

resistance or of the measuring system is achieved.

In opposition to previously known solutions of force measuring

sensors and, among other things, with respect to patents DE

199 54 164 B4 and DE 10 2006 019 942 Al, it should be cited

that:

• none of the force measuring systems based on piezoresistive

thin insulating film systems described in the prior art

comprises a device for fully and with high precision

compensating for temperature-dependent drift of the

insulation resistance;

• a wide variety of thin insulating films and multi-layer

systems having semiconductor behavior are employed, wherein

the sensitivity thereof with respect to the force-dependent

electrical conductivity or electrical resistance

deliberately by way of specific manufacturing methods,

[5 chemical substance combinations and the introduction of

impurities releasing additional electrical charge carriers,

which considerably increase the force-dependent

piezoresistive effect. Examples of such thin insulating

films or thin insulating film combinations are aluminum

titanium-nitrite, aluminum-chromium-nitrite, zirconium

oxide-nitrite or aluminum-chromium-nitrite-oxide, and many

others, which, serving as semiconductors, exhibit strong

sensitivity to the force-dependent change in resistance;

with respect to geometry and material selection, the

mechanical force transmission elements are configured in

such a way that no change in geometry or negligible

deformation of the mechanical force transmission elements

takes place, and thus a force measurement is directly

converted into an electrically measurable signal without travel or displacement errors, which is to say the thin

insulating film is the only sensor coupling member, and no

other component tolerances and mechanical disturbances enter

the measuring chain; furthermore, for example in the sensor design comprising hard metal force transmission elements serving as the electrodes (1 and 3), electrically exactly defined contact resistances are achieved between the interfaces of the metal electrodes (1 and 3), the contact resistance of which in the milliohm range is exactly constant, regardless of the applied force under which these elements are pressed together;

• the arbitrary, even miniaturized, design of the force

measuring sensors or force measuring sensor combinations,

serving as a multidimensional force measuring unit, makes an

extremely rapid, high-resolution measuring unit possible,

wherein the physical boundaries of this system are solely

electrically limited by the charge/discharge times of the

[5 measuring currents or changes in voltage of the measuring

circuit to the analog-to-digital converter. Modern

electronic signal amplification and processing circuits open

up an unprecedented performance level in dynamic force

measurement;

depending on the selected thin insulating film or thin

multi-layer insulating film system and the material

composition thereof and accordingly robust force

transmission elements, unprecedented temperature stability

of such sensors in the range of less than one hundred

degrees Celsius to 1200 degrees Celsius becomes possible;

• energy-saving applications and very cost-effective

miniaturized force measuring systems, operated by battery

over many years, become possible since the measuring

currents can be switched only briefly in active sleep mode with extremely long sleep phases, wherein very short

settling phases of the measurement system enable a very

short active duration; the mechanical robustness and wear resistance of the thin insulating film exceeds the load limit of the mechanical coupling elements, for example 2 gigapascals of compressive strength for hard metal.

The option to implement multifaceted configurations, combined

with the very high degree of freedom regarding

miniaturization, normal sizes for mechanical standard

elements, for example connecting elements such as bolts,

screws, thrust washers and the like, all the way to

applications in heavy equipment construction, is possible as a

result of this measuring technology using thin insulating

films.

[5 The exemplary embodiment at the bottom of FIG. 4 shows a

sectional illustration of the force measurement in one

direction, and that at the top of FIG. 4 shows the component

based force measurement in two directions, which is to say in

the two-dimensional space (2D) with the force components F x

and Fy.

The further exemplary embodiment according to FIG. 5 shows a

multi-dimensional sensor design by way of example, wherein

electrical force measurement takes place in a component-based

manner in the two times four dimensional space from 4

different rotation angles in the 3D space (Fx + Fy). This

electrical measuring circuit and the selected sensor design

are shown in the form of a sectional illustration, wherein an

arbitrary number of rotationally added (n-) sensor elements can be assembled; however, in the specific example here, n=4

separate units are determined for 4 rotation angles and are

intended to show the freedom of design with respect to the mechanical design and electronic evaluation options by way of example.

Description of legend

(1) electrode or shared electrode in the case of multidimensional measuring cells

(2) thin insulating film (2-n or 2.n in the case of a multidimensional design), which is to say nth thin insulating film

(3) electrode or nth electrode in the case of multidimensional sensors (3-n or 3.n in the case of a multidimensional design)

(4) reference metal electrode or nth electrode in the case of multidimensional sensors (4-n or 4.n in the case of a multidimensional design)

(5) mounting for reference metal electrode, which with a

[5 constant retaining force fixes the reference metal electrode at a constant retaining force from the two opposite directions

(6) power source I_q

(7) ammeter I or, in the case of a multidimensional design, nth ammeter of the respective force component (direction) and the associated nth current measuring channel

(8) voltmeter U or U n or, in the case of a multidimensional design, nth voltmeter of the respective force component (direction) and the associated nth voltage measuring channel (8-n or 8.n in the case of a multidimensional design)

(9) reference voltmeter U ref or U ref-m or, in the case of a multidimensional design, mth voltmeter of the respective force component (direction) and the associated mth reference voltage measuring channel (9-m or 9.m in the case of a multidimensional design)

(9) reference ammeter I ref or I ref-m or, in the case of a

multidimensional design, mth reference ammeter of the

respective force component (direction) and the associated

mth reference current measuring channel (9-m or 9.m in

the case of a multidimensional design)

(11) fixed resistance R_1 = constant of the half measuring

bridge

(12) fixed resistance R_2 = constant of the half measuring

bridge

(13) insulating film resistance R_1 of the full measuring

bridge

(14) insulating reference resistance R ref-1 of the full

[5 measuring bridge

(15) insulating resistance R_2 of the full measuring bridge

(16) insulating reference resistance R ref-2 of the full

measuring bridge

(17) insulating film resistance R_17 between the two measuring

cells placed on top of one another to make the full

measuring bridge possible [R_ >= 500 * R_1 ]

EDITORIAL NOTE

Patent No. 2016292465 Please notionally renumber claims pages as 28 to 32

Claims - PCT Article 34

1. A device for electrically measuring a force (F) comprising:

- a load cell comprising

o a first metal electrode (1) and a second metal

electrode (3) disposed opposite thereof in the

direction of the force (F) to be measured, each

being made of hard metal, steel or low-resistance

metal layers on ceramic, glass or or plastic bodies

and having contact surfaces by way of which the

force (F) to be measured can be impressed, and

having electrical resistance in the range of a few

milliohms to less than or equal to ten ohms and a

mean roughness value (Ra) of less than or equal to

400 nanometers, for forming force-independent

[5 conductivity,

o a thin insulating film (2), which is disposed between

the metal electrodes (1, 3) in a form-locked manner

and made of a material selected from the group

consisting of:

• zinc oxide,

• stochastically reduced aluminum oxide Al 2 0

where x = 2.4 to 2.8,

• silicon carbide,

• a DLC layer (diamond-like carbon),

o a reference metal electrode (4), which is disposed on

a section of the thin insulating film (2) in a

manner that is force-decoupled from the first metal

electrode (1) and tensioned with respect to the

second metal electrode (3) at a constant retaining

force by a fastening element (5);

a measuring circuit designed as a half bridge or a full

bridge, wherein

" a current path fed from a power source (6) in a

series connection runs across the first metal

electrode (1), the thin insulating layer (2) to the

second metal electrode (3), and onward across the

thin insulating layer (2) to the reference metal

electrode (4),

o a force-dependent voltage (8) is tapped between the

first metal electrode (1) and the second metal

electrode (3), the voltage dropping across the thin

insulating film (2),

o a reference voltage (9) is tapped between the second

metal electrode (3) and the reference metal

electrode (4),

o the measuring circuit forms a voltage ratio from the

[5 force-dependent voltage (8) and the reference

voltage (9), the voltage ratio representing a value

of the impressed force.

2. The device according to claim 1, characterized in that the

thin insulating film (2) is designed as a thin multi-layer

insulating film (2).

3. The device according to claim 1 or 2, characterized in that

the contact surfaces of the first and second metal

electrodes (1, 3) is designed a form fit in the range of

less than 4 micrometers across the entire contact surface.

4. The device according to one or more of claims 1 to 3,

characterized in that the first metal electrode (1), the

second metal electrode (3) and the metal electrode (4) have

at least the same strength as, or greater strength than,

the thin insulating film (2).

5. The device according to one or more of claims 1 to 4,

characterized in that a spatial distance of less than or

equal to 200 millimeters exists between the measuring

circuit and the load cell.

6. The device according to one or more of claims 1 to 5,

characterized in that the mean roughness value Ra of the

contact surfaces of the first metal electrode (1) and of

the reference metal electrode (4) are rougher at a ratio of

30:1 to 2:1 compared to the mean roughness value of the

contact surface of the second metal electrode (3), which

has a mean roughness value Ra of less than or equal to 200

nanometers.

7. The device according to one or more of claims 1 to 6,

characterized in that multiple reference metal electrodes

[5 (4) are provided on the load cell.

8. The device according to one or more of claims 1 to 7,

characterized by comprising a second load cell having the

same design, which can be positioned in the direction of an

interfering force component.

9. The device according to one or more of claims 1 to 8,

characterized in that the load cell comprises a plurality

of thin insulating films (2.1, 2.2), which electrically are

associated with a plurality of measuring circuits, and the

spatial or geometry arrangement is designed in such a way

that the magnitude and direction of the forces to be

measured are simultaneously detected as a vector quantity.

10. The device according to one or more of claims 1 to 9,

characterized in that the metal electrodes (1, 3) and the

Claims (1)

1. reference metal electrode (4) are manufactured as

   insertable bodies having freely selectable ruled geometries

   as positive and negative shapes.

   11. The device according to claim 10, characterized in that the insertable bodies are selected from the following group:

   - designed as an inside truncated cone and an outside

   truncated cone comprising lateral surfaces having the

   same shape, the thin insulating film (2) being applied

   to the lateral surface;

   - designed as cylinder surfaces, inserted into one

   another, of the outer cylinder and inner cylinder having

   thin insulating films applied to the cylinder lateral

   surface, the thin insulating film (2) being applied to

   the end face of the cylinder rings.

   12. The device according to one or more of claims 1 to 11,

   characterized in that the thin insulating film (2) is

   applied to the circumferential surface of two mutually

   connected truncated cones on the outer surface of the

   respective inner electrode, which are mounted respect to a

   precisely fitting casing made of two outer electrodes that

   are electrically insulated from one another as a negative

   shape.

   13. The device according to one or more of claims 1 to 12,

   characterized in that an electronic signal generator is

   used as the power source (6), which in a first operating

   mode operates as a regulated direct current source or in a

   second operating mode as an alternating current signal

   source, and that furthermore the measuring circuit can be

   set to the respective operating mode.

   14. The device according to one or more of claims 1 to 13,

   characterized in that mechanical transmission elements for

   passing on the force to the metal electrodes (1, 3) and the

   reference metal electrode (4) are provided, which are

   designed as shaped parts made of strong plastic materials

   or high-strength composite materials.

   15. The device according to one or more of claims 1 to 14,

   characterized in that the measuring circuit furthermore

   comprises band stop filters or band pass filters.