Measuring and testing – Dynamometers – Responsive to multiple loads or load components
Reexamination Certificate
2000-01-14
2001-11-27
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to multiple loads or load components
Reexamination Certificate
active
06321605
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an opto-mechanical sensor for providing load and/or pressure distribution data, and especially to a pressure sensor providing high spatial resolution over a large area on a surface exposed to constant or varying forces. The system can provide large quantities of information in a visual and digital format using simple and easily implemented techniques. The sensor may have a large area, of several square meters, or a small area of less than one square centimeter. The pressures to be measured may also vary greatly.
2. Prior Art
Loads and pressure distributions on surfaces have traditionally been measured using mechanical load cells for the force on the whole surface and pressure sensors incorporated into the surface for local force and pressure measurement. The load cells are made of a material, usually metal, that deforms under load and the strain is monitored using an attached strain gauge. The pressure sensors are generally mechanical in design.
One type of pressure sensor is the piston/diaphragm design where load on the pressure head is transmitted through the piston to the diaphragm causing a deflection and a consequent change in output from a strain sensor on the diaphragm. Piezoelectric films are also available for measuring dynamic load and pressure. These existing technologies have drawbacks.
Firstly, the piston/diaphragm sensors require fairly extensive modification of the surface for installation and are limited in the number that can be installed so that large areas cannot be instrumented nor can the spatial resolution be very great because of structural modifications to the surface. Every sensor must have appropriate electrical connections which further limit the number and extent of the sensors on a surface.
Piezoelectric film has the advantage over piston sensors that the surface does not require much alteration and the spatial resolution can be high for the sensor spacing. The sensors can only be used for dynamic load situations however and there is still the issue of wiring being required for each of the sensing elements in a sensor array. They are impractical for coverage of large areas at high spatial resolution because of the demands on the data acquisition system. For example a one meter by one meter array of sensors with one centimeter spatial separation implies that there are 10,000 individual sensors from which to acquire data.
Surface-area transducers using electrical components such as capacitors to measure pressure distribution are also known, for example as described in U.S. Pat. No. 4,644,801 to Kustanovich, issued Feb. 24, 1987. Such transducers also require rather complex data acquisition systems.
U.S. Pat. No. 4,599,908 to Sheridan et al., issued Jul. 15, 1986, describes a system in which a pressure deformable body has an array of holes which are each aligned with a hole in a supporting base or platen, and each of the base or platen holes is fitted with the end of an optical fiber. The upper surface of the deformable body is covered by a load receiving flexible sheet, and when the flexible sheet is subjected to loads it causes the deformable body to bulge into its holes to reduce the hole diameter. The optical fibers are connected to a receiver viewed by a video camera, and the optical fibers transmit signals to the camera which indicate the reduction in hole diameter caused by the pressure. The Sheridan et al. system has drawbacks similar to those systems having a large number of load sensors, in that the fibers have to be attached individually to the holes, and a one meter by one meter array at one centimeter spacing would require 10,000 fibers. With less fibers, the resolution will be low. The need for a fiber connection corresponding to each hole also limits the nature of the deformable body; it needs an array of holes matching those of the base, which involves substantial expense, and cannot be formed as a body having a series of slits, as may be desirable for economy.
Other pressure distribution sensors use optical fibers in the plane of the sensors and which are sensitive to bending of the fibers or to contacts made between fibers when pressed together under pressure; an example is U.S. Pat. No. 4,901,584, issued to Brunner et al. on Feb. 20, 1990.
A pressure sensor is also known from U.S. Pat. No. 3,987,668, issued to Popenoe on Oct. 26, 1976. This uses a flexible light transmitting member which, under pressure, is pushed into contact with a light absorbing member; the area of contact between the light transmitting member and the light absorbing member is recognized by the frustration of internal reflection which occurs in this area. However, this sensor is only suitable for indicating overall pressure, and it is not suitable for showing pressure distribution since any area subjected to pressure affects neighbouring areas.
SUMMARY OF THE INVENTION
The present invention provides a load sensor arrangement which, as in Popenoe, uses the frustration of internal reflection or similar means to indicate contact between a transparent member and a non-transparent member. However, in the present invention the light transmitting member is separated from the light absorbing member by spacer means which divide the area subjected to pressure into an array of cells or zones which are effectively separate so that pressure distribution over a large area can be studied. Also, unlike in Popenoe, in the present invention the transparent member is generally a rigid platen, while the light absorbing member is the flexible member subjected to pressure.
Also, unlike some other prior art sensors referred to above, apparatus of this invention does not need optical fibers, and is capable of giving load sensing information at high spatial resolution, over a large area, at comparatively low cost as compared to the Sheridan et al. arrangement. In various forms of the invention it is capable of being monitored remotely either from the same side as the base or platen, i.e. opposite to that receiving the load or pressure, or from the same side as the pressure applying medium if this is transparent, for example if it is water or air, or from the edges of a thick platen having flat and clear edge surfaces. Since no optical fibers or similar cable means are required the base or platen may be isolated from the monitoring means. This may be useful for example where it is required to allow movement between the platen and the monitoring means or where the closeness of monitoring means to the platen would disrupt fluid flow.
In accordance with the invention, apparatus for sensing the load or pressure distribution on a surface comprises:
a platen providing a surface which is stiff relative to the loads being detected;
a load receiving sheet extending over the platen surface and having an outer surface exposed to the load or pressure; and
separator means having regularly spaced apertures or gaps lying between the load receiving sheet and the platen and thin enough that loads to be detected applied to the outer surface of the load receiving sheet cause parts thereof, or parts of a sheet or layer underlying the load receiving sheet, to be pushed through the apertures or gaps and into contact with a platen surface. Areas of the load receiving sheet or of the underlying sheet or layer which contact the platen surface can be measured to indicate the pressure distribution.
Either the load receiving sheet is flexible so that it can be forced by pressure into the apertures of the separator, and/or it is provided with an underlying deformable layer which can contact the platen through the apertures. The apertures of the separator means effectively divide the area of the load receiving sheet into a series of cells or zones so that pressure or load on each such cell can be indicated.
One of the platen or load receiving sheet is a transparent member, and the apparatus preferably includes a video camera viewing the load receiving sheet or the underlying or deformable layer through the transparent member and d
National Research Council of Canada
Noori Max
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