Pressure and shear movement sensor

Abstract

The invention provides a pressure and shear movement sensor comprising a first and a second flexible carrier foil (1, 2) stacked on top one another, a spacer layer (3) arranged therebetween, and a sensing circuit. The sensing circuit comprises a source terminal (12) for connection to a voltage source, and an output voltage node (14) for voltage measurement. The sensing circuit further comprises a plurality of resistive segments (15-19) arranged on each carrier foil (1, 2), thereby forming a discontinuous resistive layer (4, 5) on each carrier foil (1, 2), with each resistive segment (15-19) of one of the two carrier foils facing a resistive segment (15-19) of the other carrier foil, thereby forming pairs of resistive segment. The sensing circuit further comprises a conductive layer (10) arranged on each carrier foil (1, 2) to connect resistive segments (15-19) to each other and / or connect resistive segments (15-19) to the source terminal (12) or the output voltage node (14). The spacer layer (3) comprises a cutout in regions which coincide with the resistive segments (15-19) of each carrier foils (1, 2), thereby forming a corresponding plurality of sensing cells. According to the invention, bending deformation of the carrier foils (1, 2) at a sensing cell bring pairs of resistive segments into contact, thereby closing the sensing circuit at least partially and enabling detection of a voltage value at the output voltage node (14), said voltage value being different for at least some of the pair of resistive segments.

Description

Pressure and Shear Movement SensorTechnical field

[0001] The present invention relates to pressure sensors, more particularly to flexible foil-based sensors capable of detecting both pressure and shear movement.Background of the Invention

[0002] Pressure sensors are widely used across industries to measure force or pressure applied to a surface. While conventional pressure sensors are effective at detecting normal forces, many fail to accurately or efficiently measure shear movements, which represent lateral forces or directional shifts on a surface. Shear force measurement is critical in applications such as slip detection, tactile sensing in human-machine interfaces, and wear analysis.

[0003] Rotational potentiometers, commonly used for measuring angular displacement, represent one approach to capturing directional movements or rotational forces. However, while they are precise in detecting rotational or angular changes, they are inherently unsuitable for detecting planar shear forces over broad and / or flexible surfaces. Rotational potentiometers are typically rigid, bulky, and restricted to fixed-axis applications, making them impractical for integration into thin, flexible, or conformal sensing systems.

[0004] Other existing shear-sensing technologies often rely on bulky or rigid sensor arrays that lack flexibility, scalability, or precision. Conventional designs generally have limited integration capabilities with flexible or curved surfaces. These limitations pose significant challenges in adopting shear-sensitive technologies in advanced and evolving fields.Object of the invention

[0005] It is therefore desirable to provide a pressure and shear movement sensor without the above described shortcomings, which is flexible and may be easily integrated to a curved surface.General Description of the Invention

[0006] The present invention provides a pressure and shear movement sensor comprising a first and a second flexible carrier foil stacked on top one another, aspacer layer arranged therebetween, and a sensing circuit. At rest, the first and a second flexible carrier foil are parallel, kept separate at a set distance by the spacer layer.

[0007] The sensing circuit comprises a source terminal for connection to a voltage source, and an output voltage node for voltage measurement, both arranged on the first flexible carrier foil. The sensing circuit further comprises a plurality of resistive segments arranged on each carrier foil, thereby forming a discontinuous resistive layer on each carrier foil, with each resistive segment of one of the two carrier foils facing a resistive segment of the other carrier foil, thereby forming pairs of resistive segment. The sensing circuit further comprises a conductive layer arranged on each carrier foil to connect resistive segments to each other and / or connect resistive segments to the source terminal and / or the output voltage node.

[0008] The spacer layer comprises a cutout in regions which coincide with the resistive segments of each carrier foils, thereby forming a corresponding plurality of sensing cells.

[0009] According to the invention, bending deformation of the carrier foils at a sensing cell brings pairs of resistive segments into contact, thereby closing the sensing circuit at least partially and enabling detection of a voltage value at the output voltage node, said voltage value being different for at least some of the pairs of resistive segments.

[0010] The voltage value being different for at least some of the pairs of resistive segments allows to discriminate between pairs of resistive segments in contact, thereby enabling to roughly locate the position of the load. As will be explained below, this configuration enables to detect and identify shear movements.

[0011] In embodiments, a subset of the resistive segments of the first carrier foil is connected to the source terminal, and a complimentary subset of the resistive segments of said first carrier foil is connected to the voltage output node. Hence current must flow through at least one pair of resistive segments from each subset to reach the output voltage node from the source terminal.

[0012] In embodiments, the conductive layer on the first flexible carrier foil comprises additional resistors, thereby defining conductive paths with different resistance values, and resistive segments which are connected to the sourceterminal are connected to the source terminal by conductive paths with different resistance values, or resistive segments which are connected to the output voltage node are connected to the output voltage node by conductive paths with different resistance values. The additional resistors thus form voltage dividers for the sensing cells, which ensures that voltage values are different for at least some of the pair of resistive segments.

[0013] In embodiments, resistive segments of the first carrier foil are arranged so as to alternate between resistive segments connected to the source terminal and resistive segments connected to the voltage output node.

[0014] In embodiments, resistive segments connected to the source terminal are connected to a first ground terminal.

[0015] In embodiments, the voltage output node is connected to a second ground terminal, preferably via a serial resistor.

[0016] In embodiments, all the resistive segments of the second carrier foil are connected to each other.

[0017] In embodiments, a non-conductive layer arranged on at least one of the carrier foils so as to isolate adjacent sensing cells from one another.

[0018] In embodiments, the carrier foils are made of plastic, preferably Polyethylene Terephthalate, Polyethylene Naphthalate, or Polyimide.

[0019] In embodiments, the resistive layers and / or conductive layers are made of electrically conductive inks, metallic layers or coatings.

[0020] In embodiments, the thickness of the carrier foils and / or the spacer layer is comprised between 0.1 - 0.3 mm;

[0021] In embodiments, the resistive segments have a triangular or semicircular shape.Brief Description of the Drawings

[0022] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:Fig.1 shows a schematic view of a first carrier foil of the inventive sensor;Fig.2 shows a schematic view of a second carrier foil of the inventive sensor;Fig.3 shows a schematic view of a cross-section of the inventive sensor;Fig.4 shows a schematic view of a cross-section of the inventive sensor with bending deformation of the carrier foils;Fig.5 shows the sensing circuit of the inventive sensor;Fig.6 shows a plot of resistance against pressure;Fig.7 shows a graph of a pressure distribution mapped against time for different resistive segments;Fig.8 shows a plot of output voltage against time in response to the pressure distribution of Fig. 7.Description of Preferred Embodiments

[0023] Figure 1 illustrates a schematic view of a first carrier foil 1 of the inventive sensor. The first carrier foil 1 comprises a sensing circuit which includes a source terminal 12 for connection to a voltage source (typically 3 - 5 V), and a first and second ground terminal 11 , 13 for connection to ground. The sensing circuit further comprises an output voltage node 14 for voltage measurement. The output voltage node 14 is connected to the second ground terminal 13 via a serial resistor 9.

[0024] The sensing circuit further comprises five resistive segments 15-19 arranged on the first carrier foil 1 along a longitudinal axis A, thereby forming a first discontinuous resistive layer 5. Resistive segments advantageously have a semicircular shape 15, 19 or a triangular shape 16-18, although other shapes may be used. A non-conductive layer 6 is arranged on the carrier foil 1 between the resistive segments 15-19 to separate them from one another.

[0025] The sensing circuit further comprises a conductive layer 10 arranged on the carrier foil 1 to connect the terminals 11 -13 to the resistive segments 15-19. The conductive layer comprises a first resistor 7 and a second resistor 8 as additional resistors. The conductive layer 10 connects the second and fourth resistive segment 16, 18 to the output voltage node 14 and the second ground terminal 13. The conductive layer 10 also connects the first, third and last resistive segments 15, 17, 19 to the source terminal and a first ground terminal 11 .

[0026] More specifically, the last resistive segment 19 is directly connected to the source terminal 12, the third resistive segment 17 is connected to the source terminal 12 via the second resistor 8, and the first resistive segment 15 is connected to the second resistor 8 (and thus the source terminal 12) via the first resistor 7.

[0027] Hence, the voltages supplied by the source terminal to the first, third and last resistive segments 15, 17, 19 is different. In other words, the conductive layer 10 forms conductive paths which connect the first, third and last resistive segments 15, 17, 19 to the source terminal with different resistance values. As will be explained below, this configuration enables detection of shear movement.

[0028] Figure 2 illustrates a schematic view of a second carrier foil 2 of the inventive sensor. Five resistive segments (also denoted 15-19) are arranged on the second carrier foil 2 along a longitudinal axis A, thereby forming a second discontinuous resistive layer 4. The location and shape of the resistive segments 15-19 of the second resistive layer 4 substantially match the location and shape of the resistive segments 15-19 of the first resistive layer 5. A conductive layer (also denoted 10) is arranged on the second carrier foil 2 to connect all the resistive segments 15-19 of the second resistive layer 4 to each other.

[0029] Figure 3 illustrates a schematic view of a cross-section of the sensor along longitudinal axis A. As it can be seen, the first carrier foil 1 and the second carrier foil 2 are stacked on top one another such that their resistive layers 5, 4 directly face each other, i.e. such that each resistive segment of the first resistive layer 5 faces a resistive segment of the second resistive layer 4, thereby forming pairs of resistive segment. A spacer layer 3 is arranged between the first carrier foil 1 and the second carrier foil 2 to separate them by a predefined distance. The spacer layer 3 has a cutout in a region which substantially coincides with the location of the resistive segments 15-19. Each pair of resistive segment forms a sensing cell defined by the spacer layer and the non-conductive layer.

[0030] The first and second carrier foil 1 , 2 have a bending stiffness such that, when no force is applied to the carrier foils, the resistive layers 4, 5 are spaced from one another. In this state the sensing circuit is thus open, with little to no voltage detectable at the output voltage node 14.

[0031] Figure 4 illustrates a view of the cross-section of Figure 3 with bending deformation of the carrier foils 1 , 2. As it can be seen, a pressure load applied onto the external surface of the carrier foils 1 , 2 brings the resistive layers 4, 5 into contact. The sensing circuit is closed if at least one of the first, third or fifth pair of segments 15, 17, 19 and one of the second or fourth pair of segments 16 or 18 come into electrical contact. In this state, voltage is detectable at the output voltage node 14. Figure 5 illustrate the sensing circuit in its fully closed state, i.e. when all five resistive segments of the first carrier foil are in contact with all five resistive segments of the second carrier foil. Due to the layout of the sensing circuit, the magnitude of the voltage and its evolution over time can be used to determine the presence of a load and possible shear movement thereof, as will be explained below.

[0032] Figure 6 shows a segment resistance in function of applied pressure load. As it can be seen, segment resistance decreases with applied pressure load in a nearly exponential way. Figure 7 shows an example of a pressure distribution on the five resistive segments P15 - P19 for different points in time t1 - 15. As it can be seen, the maximum pressure load moves uniformly from the first segment 15 at t1 to the fifth segment 19 at t5.

[0033] Figure 8 shows the output voltage at the output voltage node 14 mapped against time resulting from the pressure distribution of figure 7. As it can be seen, the movement of the load from the first segment 15 to the fifth segment 19 leads to a linear increase in output voltage. This evolution of output voltage is largely due to the conductive paths which connect the first, third and last resistive segments 15, 17, 19 to the source terminal with different resistance values.

[0034] Indeed, when the load is on the first segment 15, current flows through both the first and second resistors 7,8 before flowing through the first segment 15 and second segment 16 to the output voltage node 14. In contrast, when the load is on the third segment 17, current only flows through the second resistor 8 before flowing through the third segment 17, second segment 16 (or fourth segment 18) and output voltage node 14. The voltage detectable at the output voltage node 14 is thus lower when the load is on the first segment 15 than when the load is on the third segment 17. Likewise, when the load is on the fifth segment 19, current flows directly through the fifth segment 19 (i.e. without going through any of additional resistors 7,8), andfourth segment 18 to the output voltage node 14. Thus, the voltage detectable at the output voltage node 14 is lower when the load is on the third segment 17 than when the load is on the fifth segment 19.

[0035] Other sequences of pressure distributions are also possible and can be detected. For example, a uniform movement of the load from the fifth segment 19 to the first segment 15 would lead to a linear decrease in output voltage. The sensor may be further configured to detect various pressure distributions by adapting the layout of the additional resistors 7, 8 or adapting the electrical characteristics of the resistive segments 15-19.

[0036] The sensor may be adapted for different pressure loads by modifying the design of the cutout of the spacer layer, the resistive segments 15-19 or the nonconductive layer 6, the thickness of the carrier foils 1 , 2, the thickness of the spacer layer 3 and / or the materials of these components. The carrier foils may be made of plastic (PET, PEN, PI, ... ) or other suitable materials. The resistive layers and conductive layers may be made of electrically conductive inks, metallic layers or coatings or other suitable materials. The thickness of carrier foils 1 ,2 and spacer layer 3 may be selected based on the desired pressure range to be detected. For example the thickness of carrier foils and spacer layer may be in the range of 0.1 to 0.3 mm to detect pressure values in the range of 0.1 to 10 bar.

Claims

Claims1 . Pressure and shear movement sensor comprising a first and a second flexible carrier foil (1 , 2) stacked on top one another, a spacer layer (3) arranged therebetween, and a sensing circuit; wherein the sensing circuit comprises a source terminal (12) for connection to a voltage source, and an output voltage node (14) for voltage measurement, said source terminal (12) and said output voltage node (14) being arranged on the first flexible carrier foil (1 ); wherein the sensing circuit further comprises a plurality of resistive segments (15-19) arranged on each carrier foil (1 , 2), thereby forming a discontinuous resistive layer (4, 5) on each carrier foil (1 , 2), with each resistive segment (15- 19) of one of the two carrier foils facing a resistive segment (15-19) of the other carrier foil, thereby forming pairs of resistive segments; wherein the sensing circuit further comprises a conductive layer (10) arranged on each carrier foil (1 , 2) to connect resistive segments (15-19) to each other and / or connect resistive segments (15-19) to the source terminal (12) or the output voltage node (14); wherein the spacer layer (3) comprises a cutout in regions which coincide with the resistive segments (15-19) of each carrier foils (1 , 2), thereby forming a corresponding plurality of sensing cells; and characterized in that bending deformation of the carrier foils (1 , 2) at a sensing cell bring pairs of resistive segments into contact, thereby closing the sensing circuit at least partially and enabling detection of a voltage value at the output voltage node (14), said voltage value being different for at least some of the pairs of resistive segments.

2. Pressure and shear movement sensor according to any of the preceding claims, wherein a subset of the resistive segments of the first carrier foil (1 ) is connected to the source terminal (12), and wherein a complimentary subset of the resistive segments of said first carrier foil (1 ) is connected to the voltage output node3. Pressure and shear movement sensor according to any of the preceding claims, wherein the conductive layer (10) on the first flexible carrier foil (1 ) comprises additional resistors (7, 8), thereby defining conductive paths with different resistance values; and wherein resistive segments which are connected to the source terminal (12) are connected to the source terminal (12) by conductive paths with different resistance values; or wherein resistive segments which are connected to the output voltage node (14) are connected to the output voltage node (14) by conductive paths with different resistance values.

4. Pressure and shear movement sensor according to any of the preceding claims, wherein resistive segments (15-19) of the first carrier foil (1 ) are arranged so as to alternate between resistive segments connected to the source terminal (12) and resistive segments connected to the voltage output node (14).

5. Pressure and shear movement sensor according to any of the preceding claims, wherein resistive segments connected to the source terminal (12) are connected to a first ground terminal (11 ).

6. Pressure and shear movement sensor according to any of the preceding claims, wherein the voltage output node (14) is connected to a second ground terminal (13), preferably via a serial resistor (9).

7. Pressure and shear movement sensor according to any of the preceding claims, wherein all the resistive segments (15-19) of the second carrier foil (2) are connected to each other.

8. Pressure and shear movement sensor according to any of the preceding claims, further comprising a non-conductive layer (6) arranged on at least one of the carrier foils so as to isolate adjacent sensing cells from one another.

9. Pressure and shear movement sensor according to any of the preceding claims, wherein the carrier foils (1 , 2) are made of plastic, preferably Polyethylene Terephthalate, Polyethylene Naphthalate, or Polyimide.

10. Pressure and shear movement sensor according to any of the preceding claims, wherein the resistive layers (4, 5) and / or conductive layers (10) are made of electrically conductive inks, metallic layers or coatings.11 . Pressure and shear movement sensor according to any of the preceding claims, wherein the thickness of the carrier foils (1 , 2) and / or the spacer layer (3) is comprised between 0.1 - 0.3 mm.

12. Pressure and shear movement sensor according to any of the preceding claims, wherein the resistive segments (15-19) have a triangular or semicircular shape.

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