Measuring and testing – Dynamometers – Responsive to force
Patent
1993-02-24
1995-09-05
Chilcot, Jr., Richard E.
Measuring and testing
Dynamometers
Responsive to force
73862625, G01L 112
Patent
active
054470765
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention pertains to a force (or pressure) sensor comprised of a base containing a capacitance electrode, a cover containing a second capacitance electrode, and spacers separating these two components.
BACKGROUND ART
A capacitive force sensor is already described under DE 34 26 165 A1; this sensor measures forces by detecting a change in capacitance between the electrodes as the cover, which is designed as a membrane, is depressed.
Such existing force or pressure-sensing devices are not suited to measure large forces or high pressures because their membrane may be depressed to such a degree that it touches the opposite side. Also, specialized auxiliary equipment is required in order to transmit forces or pressures to the device. A further disadvantage results from the nonlinear relationship between capacitance and force or pressure set up in this type of device.
DISCLOSURE OF INVENTION
Improvements this invention offers over the aforementioned state-of-the-art devices include: A compact design, the capacity to accommodate very large forces and high pressures, and the establishment of a linear relationship between changes in capacitance and the force or pressure measured.
The invention achieves these improvements by choosing materials for the device's base and cover with sufficient thickness so that when a force is applied, the material of at least one these components will be compressed to such a degree that a decrease in the distance between the capacitance electrodes will result but the materials bridging the areas between the spacers are not deformed.
The spacers are distributed along the base and cover surfaces, which face each other. Their size (height or length) is very small relative to the thickness of the material comprising the base and the cover. Thus, a change in capacitance results almost exclusively from the compression of the base and/or cover material. The spacers can be constructed as many columns (each with a square cross section) arranged in a checkerboard pattern. The distance between these columns should be approximately the same as the length of their sides.
The spacers can also be constructed as U-shaped ridges on the surface of the base. Another possibility is to construct the spacers as ridges having cross sections in the shape of sections of a circle.
Further useful examples of the invention are described below and illustrated in the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 A longitudinal section of the invented capacitive force sensor,
FIG. 2 A lateral cross section of the base's interior surface and a cross-section of the spacers,
FIG. 3 A lateral cross section of a base with spacers formed as ridges,
FIG. 4 A lateral cross section of a base with spacers formed as arched ridges,
FIG. 5 A capacitive force sensor in longitudinal section. The components are made of compressible materials and shown in this section in order to demonstrate the invention's function,
FIG. 6 Similar to FIG. 5, except that in this illustration, only the base material is compressible,
FIG. 7 An applied example showing a force sensor in which the base and spacers are manufactured as a single unit,
FIG. 8 A lateral cross section of the force sensor base illustrated in FIG. 7,
FIG. 9 An applied example showing a force sensor made as two half units with half of each spacer protruding from these units. An insulating layer stretches across the entire surface between the spacers,
FIG. 10 An applied example of a force sensor with a cover made of a non-conducting material,
FIG. 11 An applied example of a force sensor in which the cover is overlain by a shielded electrode layer,
FIG. 12 A modified force sensor showing an insulating layer overlaying the cover's surface and a second insulating layer within the base.
FIG. 13 A force sensor showing a base and cover that are in mechanical and electrical contact. The longitudinal section is taken along the sensor connector leads,
FIG. 14 The same force sensor shown in FIG. 13, but illustrating the longitudinal section alo
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Chilcot Jr. Richard E.
Dougherty Elizabeth L.
Hughes Michael J.
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