MXPA98000492A - Tissue sensor system conduc - Google Patents

Abstract

The present invention relates to a sensor for the seat of a motor vehicle including a compressible layer preferably of foam disposed between two conducting sheets. In one embodiment, the capacitance between the conductive sheets is measured to determine which object and if an object is disposed in the sensor, while in another application, holes are formed through the compressible layer so that the conductive sheets can contact each other through the holes. Embodiments are described having relatively low resistivity to produce a short circuit, and an embodiment having greater resistivity in which the magnitude of the change and resistance can be used to determine the nature of an object.

Description

CONDUCTOR TISSUE SENSOR SYSTEM.

FIELD OF THE INVENTION The present invention relates generally to sensor systems using conductive tissue, and more specifically to conductive tissue sensing systems that can operate as a switch or weight sensor. BACKGROUND OF THE INVENTION There are many applications in which weight sensors can be used to facilitate a trigger system or attenuate a trigger system that automatically operates upon the occurrence of some events. One such circumstance is the deployment of safety airbags inside the vehicle. It has been widely reported that the force with which such airbags deploy can cause injury to the same persons that such airbags are considered to protect. The deployment force is especially harmful to children and other small people below a certain weight. A sensor used in combination with the airbag that registers, interprets and transmits signals to the airbag release mechanism related to the weight of the occupant currently sitting in the car seat would be very advantageous. In a sophisticated airbag release system, the rate and degree of inflation could be adjusted to occur in a proportion that is safe to the weight of the occupant of the seat so as to reduce the degree of possible injury due to high-speed deployment. BRIEF DESCRIPTION OF THE INVENTION Briefly stated, and according to a presently preferred embodiment of the invention, a sensor embedded in a vehicle seat to determine the nature of a person or object occupying the seat, includes a layer of compressible material having a plurality of openings extending through a first surface to a second surface of the layer, a first layer of conductive tissue in a first surface, a second layer of conductive tissue in a second surface, and a sensor connected to the first and second layers. second of conductive tissue to measure the electrical resistance between them to determine the nature of a person or object occupying the seat. According to another aspect of the invention, the conductive fabric layer is stretchable in one direction. According to another aspect of the invention, a layer of conductive fabric is stretchable in two directions. According to another aspect of the invention, one of the layers of conductive tissue has a greater resistivity measured in square ohms than the other layer of conductive tissue, and a sensor is connected between spaced points in the layer of conductive fabric of higher resistivity to measure the resistance between the spaced points. Although the new aspects of the invention are set forth in detail in the appended claims, the invention itself, together with other objects and their advantages can be more readily understood by reference to the following detailed description of their presently preferred embodiment, taken in conjunction with the accompanying drawings, in which: Figure 1 is a top plan view of a seat sensor according to a presently preferred embodiment of the invention. Figure 2 is a sectional view taken along lines 2-2 of Figure 1. Figure 3 is a sectional view of the sensor pad of the invention in an uncompressed state. Figure 4 is a sectional view of the sensor pad of the invention in a compressed state. Figure 5 is a diagrammatic view of a seat sensor system according to the invention, which includes a plurality of sensor pads having different characteristics. Figure 6 is a diagrammatic view of an embodiment of the invention based on the change in capacitance when compressing a foam layer.

Figure 7 is a view of the sensor pad of Figure 6 with an applied weight. Figure 7a is a sectional view taken along the lines la-la of Figure 7. Figure 8 is a plan view of an embodiment with short circuit pads located in a tissue layer. Description of the invention According to the present invention, the system can function as a switch or as a weight sensor or both. The operating band and / or function of the sensor depends on the manner in which the materials are cut, adhered, or interconnected and the relative stability of the surrounding support structure. As shown in Figures 1 and 2, the preferred basic construction of the sensor is a five layer laminate, although any suitable layer structure may be suitable. In the preferred five layer system, the basic construction includes the following elements: a first layer of conductive fabric 10; a layer of adhesive 12; a layer of compressible foam 14; a layer of adhesive 16; and a second layer of conductive fabric 18. The preferred fabric may be conductive throughout, or conductive on one side only, and may be stretchable and flexible in one direction, both directions (x and y) or in no direction. The conductivity must correspond to the properties of the other materials to produce a shot or detection in the desired band of weight. If the fabric is conductive on one side only, that side should be against the foam. The preferred adhesive must be strong enough to adhere the fabric to the foam over the entire duration of the sensor or switch. The adhesive must be applied to the foam before cutting the holes, so that where there is a hole in the foam, there is no adhesive on the fabric, as shown in figures 2 and 3. The preferred thickness of the foam, the The compression set and the mechanical configuration preferably determine the functionality of the sensor. The foam must withstand repeated compression and pressure cycles that would naturally be expected from the use of the seat. The preferred construction of the switch is based on the size and spacing of openings in the foam in the functional band. For example, using an ester-based foam having a thickness of about 6.35 mm (0.25 inch) in thickness, a foam of 0.906 kg (2 pounds) with holes or pores of about 10.16 mm ( 0.40 inch diameter) spaced at centers of approximately 2.54 mm (0.1 inch) could provide a shooting effect at around 22.65 kg (50 pounds) per square foot. Removing some of the holes, changing the diameter of the holes, changing the separation or changing the properties of the foam will produce a new trigger point in terms of weight distribution measured as pounds per square foot (4,883 kg / m2). The trigger point will also be affected and manipulated by altering the stiffness of the support structure. According to the present invention, as shown in Figure 4 in a preferred embodiment, the operation of the switch is based on the flexibility of the conductive fabric and the compressibility of the foam. In practice, the foam 14 must be compressed somewhat, and the fabric 10, 18 must enter the holes in the foam. At some point, the upper and lower tissues will touch, producing a conductor path. The switch is based on the flexibility of the support structure (top and bottom) to push the fabric into the holes in the foam enough to make contact between the two pieces of fabric. For example, if the switch is placed on the firm top of a table, it will not work, because the surface of the lower fabric will never rise through the holes in the foam to come into contact with the other surface of the fabric.

In a preferred embodiment, as shown in Figures 6, 7, and 7a, the sensor construction of the present invention is based on the capacitance effects of the fabric / foam laminate. When the two conductive layers 10, 18 are brought closer by pressure, the distance between the fabric will change and the capacitance of the assembly can be measured. The capacitance value can be calibrated to provide a weight value. This assembly requires a continuous foam surface 14 without holes, so that the two tissue surfaces can not be touched. Figure 5 represents an embodiment of the invention in which a plurality of sensors are provided in a vehicle seat to determine the nature of a package or a person occupying the seat. Each of the sensors 30, 32, and 34 is formed in any of the ways described in the application, and is positioned with respect to the seat, so that it is actuated by a person sitting on the seat or an object placed on top. For example, the sensor 30 can be placed in the seat, the sensor 32 can be arranged in the center of the seat so that it would be operated by a person seated in the seat but not by a car seat whose lanes would straddle the sensor 32, and the sensor 34 could be placed in the seat backrest. In this way, observing the signals produced or not produced by the loads applied to the three sensors, could determine the nature of the person or thing that occupies the seat. Figure 8 represents another embodiment of the invention. In this embodiment, the lower fabric layer 18 is characterized by a measurable resistivity, such as 1-10 square ohms, and the upper fabric layer 10 is selectively conductive, so pressure must be applied in some areas to create a short circuit between positions spaced in the area of inferior fabric 18. This will allow to determine the position of the loads in the sensor without the need for an array of inputs and outputs. For example, a person occupying a seat may be expected to create pressure near the center of the sensor, whereas a car seat with side rails would exert more pressure at the edges and less in the center. The central pad 40 covers a 3 x 3 square grid, and even if short circuits were created covering the nine openings, only a relatively small change in resistance would take place. However, longer conductive pads 42 and 44 covering a relatively smaller number of openings, but a greater distance would produce a greater resistance change, which would be easily detected by known means.

Claims (13)

1. CLAIMS 1. A sensor embedded in a vehicle seat to determine the nature of a person or object occupying the seat, including: a layer of compressible material having a plurality of openings extending through, from a first surface to a second surface of the layer of compressible material; a first layer of conductive fabric on the first surface; a second layer of conductive fabric on the second surface; a sensor connected to the first and second layers of conductive tissue to measure the electrical resistance therebetween to determine the nature of a person or object occupying the seat. The sensor of claim 1, wherein the layer of conductive fabric is stretchable in one direction. The sensor of claim 1, wherein the conductive fabric layer is stretchable in two directions. The sensor of claim 1, wherein the first layer of conductive fabric has a very low resistivity, measured in square ohms. The sensor of claim 1, wherein the first layer of conductive fabric has a relatively high resistivity, measured in square ohms. 6. The sensor of claim 1, wherein the first layer of conductive material includes a continuous conductive layer. The sensor of claim 1, wherein the first layer of conductive material includes a locally conductive layer having conductive regions and non-conductive regions. 8. A sensor embedded in a vehicle seat to determine the nature of a person or object occupying the seat, including: a layer of compressible material having a plurality of openings extending through, from a first surface to a second surface of the compressible material layer; a first layer of conductive fabric in the first surface having a first resistivity, close to zero; a second layer of conductive fabric in the second surface having a greater resistivity than the first layer; and a sensor connected to spaced points in the second layer of conductive fabric to measure the resistance between the points and produce a signal corresponding to the measured resistance to indicate the nature of a person or object occupying the seat. The sensor of claim 8, wherein the first layer of conductive fabric includes a plurality of conductive patches separated by regions of low conductivity. The sensor of claim 9, wherein the plurality of conductive patches covers at least two holes in the layer of compressible material. 11. A sensor embedded in a vehicle seat to determine the nature of a person or object occupying the seat, including: a layer of compressible dielectric material having a first surface and a second surface of the layer of compressible material; a first layer of conductive fabric on the first surface; a second layer of conductive fabric on the second surface; a sensor connected to the first and second layers of conductive tissue to measure the electrical capacitance therebetween to determine the nature of a person or object occupying the seat. The sensor of claim 11, wherein the layer of conductive fabric is stretchable in one direction. The sensor of claim 11, wherein the layer of conductive fabric is stretchable in two directions.