WO2020023826A1

WO2020023826A1 - Sensor array utilizing an electrically conductive foam

Info

Publication number: WO2020023826A1
Application number: PCT/US2019/043577
Authority: WO
Inventors: Bruno D. CARRARO; Eric Kozlowski
Original assignee: Magna Seating Inc.
Priority date: 2018-07-27
Filing date: 2019-07-26
Publication date: 2020-01-30

Abstract

A sensor array 18 includes an electrically conductive polyurethane foam substrate 20 and a circuit 21. The electrically conductive polyurethane foam substrate has a top surface 28 and a bottom surface 30. The circuit is printed on the top surface or the bottom surface of the electrically conductive polyurethane foam substrate. The circuit includes an interdigitated pattern 24 and conductive traces 22, 23.

Description

SENSOR ARRAY UTILIZING AN ELECTRICALLY CONDUCTIVE FOAM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. provisional patent application 62/703,910, filed on July 27, 2018, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present invention relates to a pressure sensing array that includes an electrically conductive foam for a seat assembly in an automotive vehicle.

BACKGROUND OF THE INVENTION

[0003] Automotive vehicles include one or more seat assemblies having a seat cushion and a seat back for supporting a passenger or occupant above a vehicle floor. The seat assembly is commonly mounted to the vehicle floor by a riser assembly. The seat back is typically operatively coupled to the seat cushion by a recliner assembly for providing selective pivotal adjustment of the seat back relative to the seat cushion.

[0004] Front passenger seat assemblies for automotive vehicles typically include a sensor in the seat cushion to determine the weight of an occupant in the seat assembly. These sensors are useful to optimize vehicle safety systems, such as airbag deployment systems. For example, a sensor may send the weight of an occupant to an occupant restraint controller, which may alter the intensity at which an airbag deploys depending on the weight of the occupant. For smaller individuals, the airbag may deploy at a lower intensity or not deploy at all. Piezoresistive materials and force sensing resistance inks are commonly used in sensor arrays because the electrical resistivity of these materials changes when a mechanical strain is applied. Flowever, these materials present considerable creep; i.e., they exhibit a continuous reduction in resistance while under a constant load. Examples of sensor arrays using l piezoresistive materials with considerable creep can be found in U.S. Patents 9,075,404; 9,442,614; 9,652,101 and U.S. Publication 2017/0305301. If the sensor array utilizes materials with considerable creep, the sensor array could misclassify the weight of an occupant and send an improper signal to the occupant restraint controller.

[0005] It is desirable, therefore, to provide a sensor array that does not present considerable creep.

SUMMARY OF THE INVENTION

[0006] According to one embodiment, there is provided a sensor array comprising an electrically conductive polyurethane foam substrate and a circuit. The electrically conductive polyurethane foam substrate has a top surface and a bottom surface. The circuit is printed on the top surface or the bottom surface of the electrically conductive polyurethane foam substrate. The circuit includes an interdigitated pattern.

[0007] According to another embodiment, there is provided a sensor array comprising a substrate, a circuit and an electrically conductive polyurethane foam substrate. The circuit is printed on the substrate and includes an interdigitated pattern. The electrically conductive polyurethane foam substrate is on the interdigitated pattern.

[0008] According to another embodiment, there is provided a sensor array comprising a first substrate, a second substrate, a circuit and an electrically conductive polyurethane foam substrate. The circuit comprises a first conductive trace, a second conductive trace and an interdigitated pattern. The first conductive trace is printed on the first substrate. The second conductive trace is printed on the second substrate. The interdigitated pattern is printed on the second substrate and is connected to the second conductive trace. The electrically conductive polyurethane foam substrate is on the interdigitated pattern to electrically connect the first conductive trace to the second conductive trace. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein :

[0010] Figure 1 is a perspective view of a seat assembly for an automotive vehicle;

[0011] Figure 2 is an exploded perspective view of one embodiment of a sensor array for a seat assembly;

[0012] Figure 3 is an exploded perspective view of a second embodiment of a sensor array for a seat assembly;

[0013] Figure 4 is an exploded perspective view of a third embodiment of a sensor array for a seat assembly; and

[0014] Figure 5 is an exploded perspective view of a fourth embodiment of a sensor array for a seat assembly.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0015] Figure 1 illustrates one embodiment of a seat assembly 10 for use in an automotive vehicle. The seat assembly 10 includes a seat cushion 12 and a seat back 14 operatively coupled to the seat cushion 12 for supporting a seat occupant in a generally upright seating position. The seat back 14 is typically operatively coupled to the seat cushion 12 by a recliner assembly 16 for providing pivotal movement between an upright seating position and a plurality of reclined seating positions.

[0016] The seat assembly 10 includes a sensor array 18 in the seat cushion 12 to measure the amount of force applied to the seat cushion 12 by an occupant of the seat assembly 10. In a preferred embodiment, the seat assembly 10 also includes a sensor array 18 in the seat back 14. Including the sensor array 18 in both the seat cushion 12 and the seat back 14 increases overall performance of the system.

[0017] Figure 2 illustrates one embodiment of a sensor array 18 in accordance with the present invention. The sensor array 18 includes an electrically conductive polyurethane (PU) foam substrate 20 having a top surface 28 and a bottom surface 30. Directional references employed or shown in the description, figures or claims, such as top, bottom, upper, lower, upward, downward, lengthwise, widthwise, left, right, and the like, are relative terms employed for ease of description and are not intended to limit the scope of the invention in any respect.

[0018] Preferably, the PU foam substrate 20 comprises a PU foam formulation as disclosed in U.S. Publication 2017/0320245, WO 2018/175843, or WO 2019/090048, each of which is incorporated herein by reference. The conductivity and permittivity of the PU foam substrate 20 change based on the degree of volumetric compression or deflection of the PU foam substrate 20. When compressed, the resistance of the PU foam substrate 20 decreases. When decompressed, the resistance of the PU foam substrate 20 increases. Thus, the resistance of the PU foam substrate 20 is inversely proportional to the magnitude of force applied to the PU foam substrate 20. The PU foam substrate 20 exhibits high resiliency and low hysteresis, and consequently low creep when under a constant force.

[0019] The sensor array 18 includes a circuit 21 printed onto either the top surface 28 or the bottom surface 30 of the PU foam substrate 20. The circuit 21 includes an interdigitated pattern 24 connecting two or more conductive traces 22, 23. The sensor array 18 also includes thermoplastic polyurethane (TPU) films 26 laminated onto both the top surface 28 and the bottom surface 30 of the foam substrate 20 to seal the foam substrate and circuitry 20, 21 together.

[0020] Referring to Figure 3, where like primed reference numerals represent similar elements as those described above, in a second embodiment of the invention, the sensor array 18' includes TPU combined with a non- woven carrier (TPU+Nonwoven) 32 rather than a TPU film 26 laminated onto the bottom surface 30' of the foam substrate 20'. The TPU+Nonwoven 32 reduces elongation of the sensor array 18'.

[0021] Referring to Figure 4, where like double-primed reference numerals represent similar elements as those described above, in a third embodiment of the invention, the sensor array 18" includes a circuit 21" which is printed onto a substrate 34. The substrate 34 comprises polyethylene terephthalate (PET), polymide (PI), or TPU+Nonwoven. A small piece of the electrically conductive PU foam substrate 20" is placed onto the interdigitated pattern 24", and a TPU film 26" is laminated onto the substrate 34.

[0022] Referring to Figure 5, where like triple-primed reference numerals represent similar elements as those described above, in a fourth embodiment of the invention, the sensor array 18'" includes a lower substrate 38 and an upper substrate 40. Each substrate 38, 40 comprises PET, PI, or TPU+Nonwoven. A first conductive trace 22'" is printed onto the lower substrate 38 and a second conductive trace 23'" is printed onto the upper substrate 40. The interdigitated pattern 24'" is printed on the upper substrate 40 and is connected to the second conductive trace 23'". Alternatively, the interdigitated pattern 24'" may be printed on the lower substrate 38 connected to the first conductive trace 22'". A small piece of an electrically conductive PU foam substrate 20'" is placed onto the interdigitated pattern 24'". An adhesive layer 36 attaches the upper substrate 40 to the lower substrate 38 to connect the interdigitated pattern 24'" to the first and second conductive traces 22'", 23'". Preferably, the adhesive layer 36 comprises polyurethane or polyacrylate.

[0023] In each of the embodiments, the interdigitated pattern 24 represents a single sensing cell in the sensor array 18. Although depicted with a single interdigitated pattern 24, the sensor array 18 preferably includes a plurality of interdigitated patterns 24 to measure a plurality of forces applied to the seat cushion 12 and/or seat back 14 by an occupant.

[0024] The electrically conductive PU foam substrate 20 bridges the electrical connection across the interdigitated pattern 24 to provide electrical connection between the conductive traces 22, 23. Because the resistance of the PU foam substrate 20 is inversely proportional to the magnitude of force applied to the PU foam substrate 20, the PU foam substrate 20 acts as a variable resistor between the conductive traces 22, 23.

[0025] A multiplexer (not shown) may be used to sample the signals among the individual sensing locations (i.e., from each interdigitated pattern 24) and then direct the signals to an electronic control unit (not shown) for further processing. For example, assuming the sensor array 18 includes "n" driving lines and "m" sensing lines, the multiplexer will transmit an array of (nxm) elements to the electronic control unit.

[0026] Upon receiving the data from the multiplexer, the electronic control unit may process the data depending on the intended use of the data. For example, the data may be provided to an occupant classification system to determine the weight of an occupant in the seat assembly. Preferably, the sensor array 18 may be used with the occupant classification system disclosed in U.S. Application No. PCT/US2019/42167 for "Systems and Methods for Occupant Classification," filed on July 17, 2019, which is incorporated herein by reference. Alternatively, the data may be used in advanced comfort solutions. For example, the array may be used to perform gradient calculations and thresholds on a particular seat segment relative to the H- Point of the occupant. The resulting pressure gradient relative to the Fl-Point may be used to adjust the positioning of the seat cushion and seat back to optimize occupant comfort.

[0027] The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.

Claims

1. A sensor array comprising : an electrically conductive polyurethane foam substrate having a top surface and a bottom surface; and a circuit printed on the top surface or the bottom surface of the electrically conductive polyurethane foam substrate, wherein the circuit includes an interdigitated pattern.

2. The sensor array of claim 1 further comprising a thermoplastic polyurethane sealed onto the top surface of the electrically conductive polyurethane foam substrate.

3. The sensor array of claim 2 further comprising a thermoplastic polyurethane sealed onto the bottom surface of the electrically conductive polyurethane foam substrate.

4. The sensor array of claim 2 further comprising a thermoplastic polyurethane combined with a non-woven carrier sealed onto the bottom surface of the electrically conductive polyurethane foam substrate.

5. The sensor array of claim 1 wherein the circuit includes a plurality of interdigitated patterns.

6. A sensor array comprising : a substrate; a circuit printed on the substrate, wherein the circuit includes an interdigitated pattern; and an electrically conductive polyurethane foam substrate on the interdigitated pattern.

7. The sensor array of claim 6 wherein the substrate comprises polyethylene terephthalate, polyimide, or a thermoplastic polyurethane combined with a non-woven carrier.

8. The sensor array of claim 6 further comprising a thermoplastic polyurethane sealed onto the substrate.

9. The sensor array of claim 6 wherein the circuit includes a plurality of interdigitated patterns.

10. A sensor array comprising : a first substrate; a second substrate; a circuit comprising a first conductive trace, a second conductive trace and an interdigitated pattern wherein the first conductive trace is printed on the first substrate, the second conductive trace is printed on the second substrate, and the interdigitated pattern is printed on the second substrate and is connected to the second conductive trace; and an electrically conductive polyurethane foam substrate on the interdigitated pattern to electrically connect the first conductive trace to the second conductive trace.

11. The sensor array of claim 10 further comprising an adhesive between the first substrate and the second substrate.

12. The sensor array of claim 11 wherein the adhesive comprises polyurethane or polyacrylate.

13. The sensor array of claim 10 wherein the first substrate comprises polyethylene terephthalate, polyimide, or a thermoplastic polyurethane combined with a non-woven carrier.

14. The sensor array of claim 13 wherein the second substrate comprises polyethylene terephthalate, polyimide, or a thermoplastic polyurethane combined with a non-woven carrier.