Measuring and testing – Dynamometers – Responsive to multiple loads or load components
Reexamination Certificate
2000-01-14
2001-07-31
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to multiple loads or load components
Reexamination Certificate
active
06267014
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 metre by one metre array of sensors with one centimetre 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 metre by one metre array at one centimetre 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 for indicating pressure distribution which is similar to that of the Sheridan et al. patent in using a deformable body, specifically a deformable layer of material, but avoids limitations of Sheridan et al. It differs from the latter, and some other prior art sensors, in that it does not need optical fibers, and is capable of giving load sensing information at high 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 one aspect of the invention, apparatus for sensing loads applied to a surface comprises a platen providing a continuous, unapertured surface which is stiff relative to the loads being detected, a load receiving sheet extending over the platen surface and having an outer load receiving surface, and a layer of deformable material separating the platen surface and the sheet, and which is capable of contacting the platen surface and sheet, and which is compressed in thickness when loads are applied to the sheet. The deformable layer is provided with regularly spaced voids, such as apertures or gaps or recesses, so that the deformable material bulges into these voids when compressed across its thickness. Either the platen or the sheet is a transparent member and the deformable layer is such that its area of contact with the transparent member increases as the material is compressed in thickness. The apparatus includes a means such as a video camera viewing the deformable layer directly through the transparent member, i.e. without the intermediary of optical fibers, and capable of detecting the increased area of contact between the deformable layer and the transparent member caused by loading of the sheet. “Viewing the deformable layer, etc.”, includes viewing a surface of the transparent member so as to determine its area of contact with the deformable layer; the surface viewed includes many voids.
Normally, the load receiving sheet is flexible and bends in response to loads to compress areas of the deformable layer corresponding to areas of the sheet subjected to loads. However, a simple kind of load cell could be made with a rigid load receiving sheet, in which case the measurements obtained from reduction in the void sizes would be indicative of the average load on the sheet.
The platen may be a sheet of transparent plastic material which constitutes the transparent member. Alternatively, instead of the
National Research Council of Canada
Noori Max
LandOfFree
Apparatus for sensing a load of pressure applied to a surface does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for sensing a load of pressure applied to a surface, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for sensing a load of pressure applied to a surface will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2559334