Measuring and testing – Dynamometers – Responsive to multiple loads or load components
Reexamination Certificate
2001-06-26
2003-04-08
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to multiple loads or load components
Reexamination Certificate
active
06543299
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates to transducers, apparatus and methods used for measuring forces exerted on a surface. More particularly, the invention relates to a novel force sensor array for pressure measurement and mapping which includes a fabric-like lattice of piezoresistive threads that are arranged in rows and columns, intersecting pairs of which conductively contact one another to form individual piezoresistive force sensing elements.
B. Description of Background Art
There are a wide variety of situations in which it would be desirable to measure normal forces exerted at discrete points on a surface, using such measurements, for example, to produce a map of pressures exerted on various portions of the surface by an object. Examples of such applications for utilizing pressure maps are given in the present inventor's U.S. Pat. No. 5,571,973, Nov. 5, 1996
, Multi
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Directional Piezoresistive Shear And Normal Force Sensors For Hospital Mattresses And Seat Cushions
. In that patent, the present inventor disclosed thin, planar sensors for measuring reaction forces exerted by mattresses or chair pads on the body of a recumbent or seated patient. One embodiment of the invention disclosed in the specification of the '973 patent includes a sensor comprised of a two-dimensional array of isolated sensor element pads, each consisting of a thin, flat layer formed of a non-conductive elastomeric polymer matrix filled with electrically conductive particles. A matrix of upper and lower conductive elements in electrical contact with upper and lower sides of each sensor pad enables separate measurements to be made of the electrical resistance of each pad. Pressure exerted on each pad, e.g., in response to a normal force exerted on the sensor matrix by a person's body, reduces the thickness of the sensor pad, and therefore its electrical resistance, by a bulk or volume piezoresistive effect.
The present inventor also disclosed a novel method and apparatus for measuring pressures exerted on human feet or horses' hooves in U.S. Pat. No. 6,216,545, Apr. 17, 2001
, Piezoresistive Foot Pressure Measurement.
The novel apparatus disclosed in the '545 patent includes a rectangular array of piezoresistive force sensor elements encapsulated in a thin, flexible polymer package. Each sensor element includes a polymer fabric mesh impregnated with conductive particles suspended in an elastomeric matrix such as silicone rubber. The piezoresistive mesh layer is sandwiched between an array of row and column conductor strip laminations, preferably made of a nylon mesh impregnated with printed metallic paths. Each region of piezoresistive material sandwiched between a row conductor and column conductor comprises an individually addressable normal force or pressure sensor in a rectangular array of sensors, the resistance of which varies inversely in a predetermined way as a function of pressure exerted on it, and thus enabling the force or pressure distribution exerted by an object contacting the array to be mapped.
The present invention was conceived of to provide a pressure or force sensor array of simplified construction and few components, which has the form of highly flexible fabric-like lattice which facilitates conforming the sensor array to compoundly curved surfaces, thereby facilitating mapping force or pressure distributions on such surfaces.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a two-dimensional sensor array for measuring forces exerted by an object on a surface at discrete points in a two-dimensional lattice, thereby enabling the distribution of pressure exerted by an object on a surface on which the sensor array is placed to be mapped.
Another object of the invention is to provide a two-dimensional pressure mapping sensor array which employs a lattice of elongated, intersecting piezoresistive threads.
Another object of the invention is to provide a two-dimensional pressure sensor array which includes a lattice of piezoresistive threads, intersecting regions of which form individual piezoresistive sensor elements.
Another object of the invention is to provide a piezoresistive force sensor array for measuring forces exerted by an object on discrete points of a surface on which the array is placed, thereby enabling mapping of pressure exerted on the surface by the object.
Another object of the invention is to provide a piezoresistive force sensor array which includes a lattice of intersecting piezoresistive threads, each thread having an electrically conductive core clad with a piezoresistive material, contacting regions of which piezoresistive threads form individual piezoresistive sensor elements, the electrical resistance of which varies inversely with externally applied pressure urging the intersecting threads together.
Another object of the invention is to provide a pressure sensor array having the form of a flexible fabric lattice which is readily conformable to a curved surface, the fabric lattice comprising intersecting piezoresistive resistive threads each consisting of a flexible wire core clad with a resiliently deformable piezoresistive material.
Another object of the invention is to provide a two-dimensional pressure sensor array for measuring the magnitude and location of forces exerted by an object on a surface on which the array is placed, the array comprising a fabric lattice made of intersecting piezoresistive threads, each of which includes a core made of a flexible electrically conductive wire clad with a piezoresistive elastomeric material.
Another object of the invention is to provide a piezoresistive pressure sensor array which comprises a fabric lattice made of interwoven warp and woof threads, each of which includes a flexible electrically conductive wire core wrapped with semi-conductive filaments made of a flexible fibrous material such as surface-carburized nylon fibers, intersecting regions of the warp and woof filaments forming a two-dimensional array of piezoresistive pressure sensor elements in which the surface electrical contact resistance between warp and woof strands is inversely proportional to an external force urging the intersecting strands together.
Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.
It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims.
SUMMARY OF THE INVENTION
Briefly stated, the present invention comprehends a two-dimensional array consisting of a lattice of individual force or pressure sensor elements comprising intersecting pairs of elongated, flexible strands or threads, each of which consists of a central electrically conductive wire core having a relatively low electrical resistivity, covered with a material having a relatively higher electrical resistivity. In one embodiment of the invention, each of a pair of flexible threads consists of a thin metal wire which is spirally wrapped with filaments made of nylon, the outer surface of each filament which has been carburized to make the surface electrically conductive. Preferably, the threads are arranged into two parallel planar sets; one set of threads forming parallel rows, and another set of threads forming parallel columns perpendicular to the rows. In one embodiment of the invention, row and column thread sets are arranged in two separate contacting plane
Chapin William L.
Noori Max
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