Force sensing device

Abstract

A force sensing device (201) comprising: a first electrode layer (202) comprising a material having a first electrical resistivity; and a second electrode layer (203) comprising a pressure sensitive material having a second electrical resistivity. The second resistivity is higher than the first resistivity. The first electrode layer and the second electrode layer are arranged separately and configured to be bonded together under the effect of an applied force. A first conductive material is applied to the first electrode layer to produce a first regulator layer (204), and a second conductive material is applied to the second electrode layer to produce a second regulator layer (205). The first conductive material and the second conductive material each include a material having a substantially low resistivity. The low resistivity is lower than the first resistivity and the second resistivity such that a current flow between the first conductive material and the second conductive material depends on a contact area between the first regulator layer and the second regulator layer when the first conductive material and the second conductive material contact under the action of an applied force.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to UK patent application number 2203792.3 filed on March 18, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a force sensing device and an electronic device comprising the force sensing device. Background Art

[0004] Force sensing devices are used in many applications and can be provided in many different shapes, sizes and with different technologies, each with their own limitations.

[0005] A limitation of existing force sensing devices is that conventional force sensors typically use contact resistance (the resistance generated at the contact point when parts are connected) as the key mechanism by which the changing resistance can be generated. In this case, these types of force sensors are sensitive to changes in mechanical interface materials (such as, but not limited to, hardness and roughness).

[0006] This can cause stability issues for the force sensor because the output of the sensor depends on how these mechanical properties change as the surrounding environment changes. An example of such an environment could be a constant force applied while increasing the ambient temperature. This will result in a change in the measured sensor resistance as the change in mechanical material properties changes the contact resistance. Other environments or scenarios can produce similar results.

[0007] There therefore remains a need for alternative force sensing devices that avoid these problems and that do not rely on contact resistance between components. Summary of the invention

[0008] According to one aspect of the present invention, a force sensing device is provided, wherein a first electrode layer comprises a material having a first resistivity; a second electrode layer comprises a pressure-sensitive material having a second resistivity, the second resistivity being higher than the first resistivity, and the first electrode layer and the second electrode layer are arranged separately and configured to be combined together under the action of an applied force; and a first conductive material is applied to the first electrode layer to produce a first regulator layer, and a second conductive material is applied to the second electrode layer to produce a second regulator layer; wherein the first conductive material and the second conductive material each comprise a material having a substantially low resistivity, the low resistivity being lower than the first resistivity and the second resistivity, so that when the first conductive material and the second conductive material are in contact under the action of an applied force, the current flow between the first conductive material and the second conductive material depends on the contact area between the first regulator layer and the second regulator layer.

[0009] Embodiments of the present invention will be described by way of example only with reference to the accompanying drawings. The detailed embodiments illustrate the best mode known to the inventor and provide support for the claimed invention. However, they are merely exemplary and should not be used to interpret or limit the scope of the claims. Their purpose is to provide teachings to those skilled in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG1 shows a contact resistance-based construction of an existing force sensing device;

[0011] Figure 2 The contactless resistive force sensing device configuration is shown;

[0012] Figure 3 A top view showing one embodiment of a contactless resistive force sensing device arrangement;

[0013] Figure 4 Shows Figure 3 Another plan view of the arrangement of the contactless resistive force sensing device; and

[0014] Figure 5 An example electronic device utilizing the force sensing apparatus of the present invention is shown. DETAILED DESCRIPTION

[0015] Figure 1

[0016] The present application proposes a force sensing device that eliminates or minimizes the contact resistance component of such a force sensing device, thereby improving the stability of the sensor independent of fluctuating and changing environmental conditions surrounding the sensor.

[0017] FIG1 shows a contact resistance based force sensing device 101 consistent with conventional devices. In conventional force sensors, a low or medium resistivity electrode 102 is combined with a high resistance base layer 103.

[0018] The example in Figure 1 shows a simplified side view configuration of a typical contact resistance based force sensing device 101. The contact resistance based sensor configuration of Figure 1 includes two sides of an interface, a first side including a low or medium resistivity electrode 102, which further includes a positive voltage electrode and a ground electrode.

[0019] The second side of the force sensing device 101 includes a high resistivity material having the desired resistivity to make contact resistance a critical mechanism in such a sensor design.

[0020] In use, a force is applied to the force sensing device 101 and current flows when the electrode 102 contacts the substrate 103. The extent to which the current flows is controlled by the pressure at the interface between the electrode 102 and the substrate 103, which is generated by the applied force. This conventional configuration is very sensitive to changes in the mechanical properties of the interface material used.

[0021] This is due to the fact that the force sensing device is based on contact resistance, which occurs at the contact point at the interface between the electrode 102 and the substrate 103 when the materials are pressed together. The applied force affects the number of micro-contacts between the two surfaces of the electrode and the substrate.

[0022] The main problem with this type of prior art arrangement is that while the resistivity of the material changes when force is applied, the contact resistance changes as the force sensing device experiences environmental changes or different scenarios. For example, at higher temperatures, the component material may be softer, which affects the contact resistance based on the hardness of the material. In one example, if the hardness of the material decreases by thirty percent (30%), the contact resistance decreases by approximately thirty percent (30%). This is a significant and undesirable performance change that is difficult for firmware or software solutions to overcome.

[0023] Thus, FIG. 1 shows a contact resistance based force sensing device having a low to medium resistivity layer including interdigitated fingers, and a high resistivity layer (eg, a high resistivity layer including a quantum tunneling composite material).

[0024] Figure 2

[0025] In order to provide a force sensing device that is less sensitive to temperature, the invention described herein eliminates the electrical resistance at the interface between materials that touch across the air gap present in the force sensing device.

[0026] Figure 2A simplified side view configuration of a contactless resistive force sensing device is shown.

[0027] The force sensing device 201 includes a first electrode layer 202 and a second electrode layer 203. Each electrode layer provides an alternate side of an interface that is configured to come together and contact to provide an electrical output in response to an applied force.

[0028] The force sensing device 201 also includes a first moderator layer 204 and a second moderator layer 205. In this embodiment, the electrode layer 202 includes a material having a first resistivity, and the electrode layer 203 includes a pressure-sensitive material having a second resistivity. The first resistivity is medium or low, and the second resistivity is high compared to the first resistivity. In this embodiment, the electrode layer 202 and the electrode layer 203 are arranged to be separated from each other and separated by an air gap 206, and are configured to be combined together when an applied force is applied to the force sensing device 201. The air gap 206 is located between the first moderator layer 204 and the second moderator layer 205.

[0029] The regulator layer 204 includes a first conductive material applied to the electrode layer 202 , while the regulator layer 205 includes a second conductive material applied to the electrode layer 203 .

[0030] In this embodiment, the regulator layer 204 is in close contact with the electrode layer 202 , which in this context is considered to indicate a lack of contact resistance between the interface of the electrode layer and the regulator layer. Similarly, the regulator layer 205 is in close contact with the electrode layer 203 .

[0031] In this embodiment, the air gap 206 separates the two sides of the interface, and the electrode layer 202 and the electrode layer 203 are arranged at a certain distance. In this way, the regulator layer 204 and the regulator layer 205 are also arranged at a certain distance from each other. In addition, the electrode layer 202 and the electrode layer 203 are respectively arranged on a first substrate 207 and a second substrate 208. The substrates are spaced apart by conventional spacing elements or the like, which ensures that the air gap 206 is maintained in the absence of applied force.

[0032] In this embodiment, the regulator layer 204 and the regulator layer 205 are properly aligned to ensure that contact between the regulator layer 204 and the regulator layer 205 only occurs in response to a force applied to the force sensing device, when the air gap 206 is reduced and minimized.

[0033] In this embodiment, the regulator layers 204 and 205 have very low resistivity. In one embodiment, this is typically less than 10 -7The resistivity value of ohm-meter (Ωm) means that when the regulator layer 204 and the regulator layer 205 are in contact with each other in a non-tight manner, the contact resistance is extremely small because its absolute value depends on the sum of the resistivities of the contacting sides of the interface. If one side of the force sensing device has a high resistance (as in some conventional systems), this resistance dominates the overall, resulting in a large contact resistance. Therefore, in this embodiment, since both sides of the interface have a low resistance, the sum of the resistivities is also low. In this way, by introducing the low-resistivity regulator layers 204 and 205 to provide a contact interface between the two electrodes, the force sensing device described herein has essentially no contact resistance.

[0034] By introducing the regulator layer 204 and the regulator layer 205, the resulting force sensing device cannot be based solely on contact resistance, otherwise an electrical short circuit will occur when the two opposite sides of the interface come into contact. Therefore, the electrode layer 203 needs to have a high resistivity on the opposite side of the regulator layer 203 relative to the interface. Typically, the regulator layer 203 also includes smaller features that are not limited in shape or distribution. Instead, the regulator layer 204 may include a series of patterns. In one embodiment, such a pattern may be substantially similar to the regulator layer 203. Alternative arrangements may also be utilized, but in various cases, the regulator layer 203 and the regulator layer 204 are configured to provide a unique contact at the interface between the two halves of the force sensing device.

[0035] In use, when a force is applied to the upper surface 209 of the force sensing device 201, the electrode layer 202 and the regulator layer 204 are brought towards the regulator layer 205 and the electrode layer 203. The force sensing device 201 is connected to a circuit so that current can flow when the regulator layer 204 and the regulator layer 205 are in contact. The extent to which the current flows is not controlled by the pressure at the contact interface, but by the macroscopic contact area. This ensures that the construction of the force sensing device 201 is insensitive to changes in the mechanical properties of the materials used at the contact interface (the point where contact is made).

[0036] In order to ensure that the force sensing device exhibits a change in resistance relative to force, it is necessary to have a macroscopic contact area that changes with the change in force at the contact interface. This is different from the microscopic "real" contact area change observed in traditional force sensing devices based on contact resistance. The macroscopic contact area is defined as the area of ​​the air gap that is small enough for the regulator layer 204 and the regulator layer 205 to be considered in contact.

[0037] The increased macroscopic contact area that changes with the applied force results in an increased number of parallel current paths through the high resistivity material of the electrode layer 203. Therefore, the increased number of parallel current paths will result in a decrease in the total resistance between the first electrode layer 203 and the second electrode layer 204.

[0038] Therefore, the force sensing device 201 provides a solution by removing the high resistivity material of the electrode layer 203 so that it is no longer a direct contact at the contact interface, and replacing it with a corresponding regulator layer 205 that provides a lower resistivity to achieve these effects.

[0039] Figure 3

[0040] Figure 3 A top view of a force sensing device 201 is shown in FIG. 2 , showing example embodiments and arrangements of an electrode layer 202 and a regulator layer 204 .

[0041] In this embodiment, the first conductive material of the regulator layer 204 includes a silver-based material, such as a silver-based ink. The material with the first resistivity of the electrode layer 202 includes a carbon-based material.

[0042] In this embodiment, the first conductive material comprising the regulator layer 204 is Figure 3 The printed pattern shown is arranged in the form of a plurality of dots 301 in this particular embodiment, but it will be appreciated that alternative patterns may also be used. In an alternative embodiment, for example, the printed pattern comprises a plurality of interdigitated fingers.

[0043] In this embodiment, the electrode layer 202 includes a plurality of interdigitated fingers 302. In embodiments where the printed pattern further includes a plurality of interdigitated fingers, it will be appreciated that each of the plurality of interdigitated fingers may be substantially similar and aligned with one another.

[0044] Figure 4

[0045] Figure 4 Another plan view from the underside of the force sensing device 201 is shown in FIG. The figure shows the arrangement of the regulator layer 205 and the electrode layer 203 .

[0046] In this embodiment, the second conductive material of the regulator layer 205 comprises a silver-based material, such as a silver-based ink. This material may be substantially similar to the conductive material of the regulator layer 204. The pressure-sensitive material of the electrode layer 203 comprises a quantum tunneling material, such as available from the applicant Peratech Holdco Ltd under the trade name Quantum tunneling composite materials.

[0047] In this embodiment, the regulator layer 205 is provided in the form of a printed pattern, and as shown in the figure, the printed pattern includes a plurality of dots 401, which correspond to the aforementioned reference Figure 3A plurality of dots 301 of the regulator layer 204 is depicted. The dot pattern prevents the force sensing device from shorting when the regulator layer 204 and the regulator layer 205 are in contact, so that the force forces the current to follow a path within the higher resistance material of the electrode layer 203.

[0048] In this embodiment, a silver-based ink dot pattern is printed onto Figure 3 The dots are shown arranged in an aligned quantum tunneling material. In this embodiment, this provides a silver-to-silver contact which cancels contact resistance by ensuring a parallel path is created between the dots, allowing current to flow through the high resistivity material.

[0049] This actually gives the effect of increasing the number of parallel resistors in the circuit. Resistance decreases as the number of parallel resistors increases, and therefore the force sensing device causes the resistance to decrease.

[0050] Figure 5

[0051] Figure 5 A typical electronic device 501 including a keyboard 502 is shown according to an embodiment of the present invention.

[0052] In this embodiment, electronic device 501 can be a desktop computer, a laptop computer or any other suitable type of electronic device that can utilize a keyboard. Keyboard 502 includes a plurality of keys 503, and a user can utilize keys 503 to provide input to electronic device 501, and then provide output to display 504 of electronic device 501.

[0053] In this embodiment, each of the plurality of keys 503 includes a force sensing device according to the present invention as described herein. The force sensing device can be used as part of a keyboard membrane, wherein a force-sensitive response is provided when a force is applied to any of the plurality of keys 503. Thus, the force sensing device described herein can provide a more appropriate and stable response even when environmental conditions change.

Claims

1. A force sensing device, comprising: a first electrode layer comprising a material having a first resistivity; a second electrode layer including a pressure-sensitive material having a second resistivity, the second resistivity being higher than the first resistivity, and the first electrode layer and the second electrode layer being separately arranged and configured to be bonded together under the action of an applied force; as well as a first conductive material applied to the first electrode layer to produce a first regulator layer, and a second conductive material applied to the second electrode layer to produce a second regulator layer; in The first conductive material and the second conductive material each include a material having a substantially low resistivity, which is lower than the first resistivity and the second resistivity, so that when the first conductive material and the second conductive material are in contact under the action of an applied force, the current flow between the first conductive material and the second conductive material depends on the contact area between the first regulator layer and the second regulator layer. 2 . The force sensing device of claim 1 , further comprising an air gap between the first regulator layer and the second regulator layer.

3. The force sensing device according to claim 1 or 2, wherein: The first conductive material includes a silver-based material.

4. The force sensing device according to any one of claims 1 to 3, wherein: The second conductive material includes a silver-based material.

5. The force sensing device according to any one of claims 1 to 4, wherein: The current flow includes a plurality of parallel paths configured to reduce a total resistance between the first electrode layer and the second electrode layer.

6. A force sensing device as claimed in any preceding claim, wherein: The material having a first resistivity includes a carbon-based material.

7. A force sensing device as claimed in any preceding claim, wherein: The pressure-sensitive material includes a quantum tunneling material.

8. A force sensing device as claimed in any preceding claim, wherein: The first electrode layer and the second electrode layer are disposed on a first substrate and a second substrate, respectively.

9. A force sensing device as claimed in any preceding claim, wherein: The first conductive material is provided in the form of a printed pattern.

10. The force sensing device of claim 9, wherein: The printed pattern includes a plurality of interdigitated fingers.

11. The force sensing device of claim 9, wherein: The printed pattern includes a plurality of dots.

12. A force sensing device as claimed in any preceding claim, wherein: The first electrode layer includes a plurality of interdigitated fingers.

13. An electronic device comprising the force sensing device according to any one of the preceding claims.

14. The electronic device of claim 13, comprising an electronic keyboard.

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