Measuring system

A measuring system in which flexible mats of individual cells are distributed in rows and columns of a matrix are individually pollable for converting mechanical pressures applied locally on surfaces of the mats, into electrical signals. Each cell constitutes a capacitor with capacitance that varies with the applied mechanical pressure. A source of voltage is connectable to each cell, and each cell has an upper surface and a lower surface. Pressure is applied to the upper surface, and a dielectric is positioned between the upper surface and the lower surface. The upper surface has a plurality of parallel strip-shaped areas with projections, whereas the lower surface has a plurality of parallel electrically conductive strip-shaped areas which extend at right angles to the first strip-shaped areas on one side of the dielectric to form a capacitor cell at each intersection. The intersections deforms resiliently under applied pressure to vary the capacitance under pressure.

The invention concerns a measuring system, preferably in the form of a 
stage made out of flexible mats or individual cells. 
A measuring system of this type is known (German OS No. 2,529,475 and 
German OS No. 3,642,088). The individual cells in the system convert 
mechanical pressure into an electric signal by varying their capacitances 
in that each cell is a capacitor and the pressure varies the distance 
between the upper and lower surface of the cell and hence its capacitance. 
Many measurement applications require several sensors per square 
centimeter. When the upper surface is only 1 to 2 mm away from the lower 
surface, the pressure can vary the capacitances of the cells only 
slightly, on the order of fractions of a picofarad (pF). 
The object of the invention is to improve the known measuring system to the 
extent that each measuring point will have a considerably higher basic 
capacitance and accordingly a wider range of variation in its capacitance 
subject to pressure. 
Thus the lower and/or the upper surface of each cell has a projection that 
tapers in toward the capacitor's dielectric, that is electrically 
conductive at least along its surface, and that can also be a rib that 
extends in one direction and, when pressure is applied, the projections 
are forced against the dielectric, which is electrically insulating, and 
flattened. This procedure increases the surface of the capacitor and hence 
its capacitance, and the dielectric, which can be a sheet mounted between 
the upper and lower surfaces, can in practice be as thin as desired, 
considerably increasing the range of capacitances on the order of several 
nanofarads (nF). Furthermore, when pressure is applied, the distance 
between the sloping and tapering surfaces and the other surface decreases, 
additionally increasing the capacitance. Preliminary tests indicate 100 
times more increments in the range of capacitance than with generic 
sensors. The resulting increase in the signal-to-noise ratio and extension 
of the range of measurement are of particular advantage. 
In one preferred embodiment of the invention the projections that taper in 
toward the dielectric are mounted on only one surface and both the 
dielectric and the other surface are intact sheets, the latter being 
electrically conductive on the whole as well as being coated intactly 
electrically conductive in the form of a single counter-electrode, in 
which case each projection is to be electrically polled individually or 
all the projections in one cell individually. It is on the other hand also 
possible instead of an intact contact for the surface that does not have 
the projections to have many separate conducting coatings that dictate the 
geometry of the cells, in which case the surface with the projections will 
be coated electrically intact and connected on the whole to one pole of 
the source of voltage. It is of course also possible to provide a separate 
electric supply line for one cell on both the upper and lower surface. It 
is of particular advantage for the projections to be in the form of a cone 
or truncated pyramid. 
In an alternative embodiment of the invention, however, there are several 
parallel ribs that taper in toward the dielectric on one surface, whereby 
the other surface of each cell has ribs that extend at an angle and 
preferably a right angle to the ribs on the other side. This embodiment is 
easy to obtain by providing several parallel strip-shaped areas with the 
projections on one side, whereas the other surface has several parallel 
also electrically conductive strips that extend at an angle and preferably 
a right angle to the strip-shaped areas on the other side of the 
dielectric, creating a region of intersection in each capacitor in the 
form of a cell. In this embodiment, accordingly, each strip-shaped area in 
the overall matrix-like measuring system is in itself electrically 
conductive at its surface and has a separate electric connection. Thus, 
the cells in the vicinity of the intersection of the two strip-shape areas 
can be activated by selecting one strip-shaped area on the upper surface 
and another extending at an angle to it on the lower surface. 
Several preferred embodiments of the invention will now be described with 
reference to the drawing, wherein 
FIG. 1a is a schematic section through a mechanically unstressed cell from 
a measuring system in accordance with the invention, 
FIG. 1b illustrates the cell in FIG. 1a subject to mechanical stress, 
FIG. 1c is a schematic top view of the contact areas on/the upper surface 
of the cell in the dielectric, 
FIG. 1d is the same view as FIG. 1c although during the mechanical stress 
represented in FIG. 1b, 
FIG. 2 illustrates another embodiment of a cell, 
FIG. 3 is an exploded view of another embodiment of a measuring system with 
many cells, 
FIG. 4 is an exploded view of another embodiment of a cell, 
FIG. 5 is an exploded view of another embodiment of a cell, 
FIG. 6 is a schematic perspective representation of another embodiment of a 
measuring system with strip-shaped areas that intersect in the form of a 
matrix, 
FIG. 7 is a schematic representation of another embodiment of a measuring 
system with many cells, 
FIG. 8 is a schematic perspective view of one alternative to the embodiment 
illustrated in FIG. 6 but with projections in the form of parallel ribs, 
FIG. 9 is a perspective view of one embodiment of the ribs in the measuring 
system illustrated in FIG. 8, 
FIG. 10 is a perspective view of another embodiment of the rib-shaped 
projections in the measuring system illustrated in FIG. 8, and 
FIG. 11 is a section through the system illustrated in FIG. 9.

A measuring system 20 (FIG. 3) comprises many cells 21 (FIG. that 
accommodate mechanical pressures on their surface 22 and convert them into 
electric signals. The surface 22 in question comprises the upper surface 
23 of measuring system 
The overall function of system will now be described with reference to the 
cell illustrated in FIG. 1. Its upper surface 23 has a number of 
projections 25 that taper in toward a dielectric 24, that are electrically 
conductive at the surface, and that deform resiliently subject to 
pressure. 
The lower surface 26 in the illustrated embodiment is a flat sheet that is 
entirely electrically conductive, at least the area that comes into 
contact with dielectric 24. The upper and lower surfaces are connected by 
way of connectors 27 to an unillustrated source of voltage. FIGS. 1a and 
1c illustrate the cell with no pressure applied to the surface 22 of its 
upper surface 23 and FIGS. 1b and 1d illustrate it with the surface 
subject to pressure. It will be evident that, when the cell is subject to 
pressure, projections 25 become resiliently deformed and produce areas 28 
of contact with dielectric 24 that are larger than the areas 29 (FIG. 1c) 
characteristic when no pressure is being applied to upper surface 23. 
Subjecting the cell to pressure accordingly increases both the active 
surface of the cell and hence the capacitance of the capacitor it 
represents. Changes in capacitance can easily be measured. 
FIG. 2 illustrates an alternative embodiment wherein the projections are in 
the form, not of cones, pyramids, or frusta, but of knobs. These 
projections are preferably made of conductive silicon rubber. 
In the embodiment illustrated in FIG. 3 it will be evident that upper 
surface 23, at least in the vicinity of projections 25, is on the whole 
connected to an electric connector 27. Lower surface 26 on the other hand 
is provided with a more or less rectangular coating that dictates the 
geometry of each cell 21 and that is connected by way of a separate 
connector 31 and of a schematically illustrated electronic switch 32 to 
second electric connector 27, allowing each cell to be polled. 
FIGS. 4 and 5 illustrate various ways of establishing contact with the 
upper surface 23 of the embodiment illustrated in FIG. 1. Thus, either an 
intersecting grid 33 or a rectangular border 34 around each cell can be 
imprinted on dielectric 24 and connected to electric connectors 27 in a 
system like that illustrated in FIG. 3. The cells 21 illustrated in FIGS. 
4 and 5 can of course also be employed in the embodiment illustrated in 
FIG. 7. 
One surface, the upper surface for example, of the embodiment illustrated 
in FIG. 6, has several parallel strip-shaped areas 35 with projections. 
The other surface has several also parallel strip-shaped areas 36 that 
extend at an angle and preferably at a right angle to strip-shaped areas 
35 on the other side of dielectric 24. The areas that face dielectric 24 
are, at least at the surface, electrically conductive, and one cell in the 
form of a capacitor is created at each intersection of strip-shaped areas 
35 and 36. It is of course also possible to provide at least one 
electrically conductive surface of a strip-shaped area 35 or 36 with a 
dielectric in the form of an insulating layer instead of dielectric 24. 
Instead of the individual pyramidal or frustal projections represented in 
FIGS. 1 through 7, it is also possible in a system that employs 
strip-shaped areas as illustrated in FIG. 6 to provide the areas with a 
number of parallel ribs that taper in toward the dielectric. A single rib 
can of course also be employed instead of several ribs. The areas on the 
upper surface are labeled 40 in FIG. 8 and those on the lower surface with 
41. FIGS. 9 and 10 are perspective views of areas 40 of various shapes. It 
will be evident that the strip-shaped area 40 on the upper surface has a 
number of ribs 41 with a triangular cross-section (FIG. 9) or of ribs 42 
with a semicircular cross-section (FIG. 10). Here again, as in the 
embodiment illustrated in FIG. 6, there can be a dielectric 24 or there 
can be no dielectric and at least one surface of upper strip-shaped areas 
40 or of lower strip-shaped areas 41 can be provided with an electrically 
insulating coating 43 that acts as a dielectric. Either system will result 
in a cell in the form of a capacitor at each intersection.