FORCE ATTENUATOR FOR FORCE SENSOR

Abstract

Described herein is a force attenuator for a force sensor. The force attenuator can linearly attenuate the force applied on the force sensor and therefore significantly extend the maximum sensing range of the force sensor. The area ratio of the force attenuator to the force sensor determines the maximum load available in a linear fashion.

Claims

1. A force attenuated force sensor, comprising: a force attenuator comprising a deformable slab having two opposing surfaces, wherein the force attenuator defines a surface area for receiving an applied force; a cavity formed on one of the two opposing surfaces of the deformable slab; and a force sensor arranged in the cavity, wherein the force sensor defines a surface area for receiving the applied force, and wherein a ratio of the surface area of the force sensor to the surface area of the force attenuator has a linear relationship with the sensitivity attenuation of the force sensor.

2. The force attenuated force sensor of claim 1, wherein the deformable slab and the force sensor are configured for mounting on a solid surface.

3. The force attenuated force sensor of claim 1, wherein the deformable slab is made of rubbery material.

4. The force attenuated force sensor of claim 1, wherein the force attenuator further comprises a solid non-deformable slab disposed on the deformable slab.

5. The force attenuated force sensor of claim 4, wherein the solid non-deformable slab is disposed on a surface of the deformable slab opposite to a mounting surface.

6. The force attenuated force sensor of claim 1, wherein the force sensor is a microelectromechanical system (MEMS) force sensor.

7. The force attenuated force sensor of claim 6, wherein the MEMS force sensor is a chip scale packaged MEMS force sensor comprising a piezoresistive sensing element.

8. The force attenuated force sensor of claim 6, wherein the MEMS force sensor is a chip scale packaged MEMS force sensor comprising a piezoelectric sensing element.

9. The force attenuated force sensor of claim 6, wherein the MEMS force sensor is a chip scale packaged MEMS force sensor comprising piezoresistive and piezoelectric sensing elements.

10. The force attenuated force sensor of claim 7, wherein the chip scale packaged MEMS force sensor comprises a sealed cavity.

11. The force attenuated force sensor of claim 7, further comprising a package substrate, wherein the chip scale packaged MEMS force sensor is electrically and mechanically connected to the package substrate.

12. The force attenuated force sensor of claim 11, wherein the chip scale packaged MEMS force sensor and the package substrate are arranged in the cavity.

13. The force attenuated force sensor of claim 1, wherein the sensitivity attenuation of the force sensor increases as the area ratio increases.

14. The force attenuated force sensor of claim 1, wherein the sensitivity attenuation of the force sensor decreases as the area ratio decreases.

15. The force attenuated force sensor of claim 1, wherein the deformable slab defines a cylindrical shape.

16. The force attenuated force sensor of claim 1, wherein the two opposing surfaces of the deformable slab are parallel surfaces.

17. A force attenuator, comprising: a deformable slab having two opposing surfaces, wherein the force attenuator defines a surface area for receiving an applied force; and a cavity formed on one of the two opposing surfaces of the deformable slab, wherein the cavity is configured to accommodate a force sensor, wherein a ratio of a surface area of the force sensor to the surface area of the force attenuator has a linear relationship with the sensitivity attenuation of the force sensor.

18. The force attenuator of claim 17, wherein the force sensor is a microelectromechanical system (MEMS) force sensor.

19. The force attenuator of claim 17, wherein the deformable slab is made of rubbery material.

20. The force attenuator of claim 17, wherein the force attenuator further comprises a solid non-deformable slab disposed on the deformable slab.

21. The force attenuator of claim 20, wherein the solid non-deformable slab is disposed on a surface of the deformable slab opposite to a mounting surface.

22. The force attenuator of claim 17, wherein the two opposing surfaces of the deformable slab are parallel surfaces.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0020] The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views. These and other features of will become more apparent in the detailed description in which reference is made to the appended drawings wherein:

[0021] FIG. 1 illustrates a perspective view of an example force attenuator including a cavity that accommodates a force sensor.

[0022] FIG. 2 illustrates a cross sectional view of the force attenuator of FIG. 1 applied to an example chip scale packaged MEMS force sensor including a piezoresistive sensing element.

[0023] FIG. 3 illustrates a cross sectional view of the force attenuator of FIG. 1 applied to another example chip scale packaged MEMS force sensor including both piezoresistive and piezoelectric sensing elements.

[0024] FIG. 4 illustrates a cross sectional view of the force attenuator of FIG. 1 applied to yet another chip scale packaged MEMS force sensor including a sealed cavity and a piezoresistive sensing element.

[0025] FIG. 5 illustrates the linear relationship between force attenuation and the surface area ratio of the force attenuator to the force sensor.

DETAILED DESCRIPTION

[0026] The present disclosure can be understood more readily by reference to the following detailed description, examples, drawings, and their previous and following description. However, before the present devices, systems, and/or methods are disclosed and described, it is to be understood that this disclosure is not limited to the specific devices, systems, and/or methods disclosed unless otherwise specified, and, as such, can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0027] The following description is provided as an enabling teaching. To this end, those skilled in the relevant art will recognize and appreciate that many changes can be made, while still obtaining beneficial results. It will also be apparent that some of the desired benefits can be obtained by selecting some of the features without utilizing other features. Accordingly, those who work in the art will recognize that many modifications and adaptations may be possible and can even be desirable in certain circumstances, and are contemplated by this disclosure. Thus, the following description is provided as illustrative of the principles and not in limitation thereof.

[0028] As used throughout, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a sensing element can include two or more such sensing elements unless the context indicates otherwise.

[0029] The term comprising and variations thereof as used herein is used synonymously with the term including and variations thereof and are open, non-limiting terms.

[0030] Ranges can be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent about, it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0031] As used herein, the terms optional or optionally mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0032] The present disclosure relates to a force attenuator with a cavity designed to fit a force sensor inside the cavity. The force attenuators described herein can optionally be used when the load on a force sensor (e.g., MEMS force sensor) is expected to be equal to or greater than about 10 Newtons (N). For example, this disclosure contemplates that the force attenuators described herein can be used to allow the use of a force sensor (e.g., MEMS force sensor) in applications including, but not limited to, automotive applications (e.g., car seat/passenger weight sensing), medical applications (e.g., patient bed monitoring), or weight scales (e.g., body weight, vehicle weigh stations, etc.). The force attenuator acts as a force transformer and adapts the same force sensor for use in applications with different maximum load requirements. As described herein, the force attenuator can be used to increase the maximum load of a given force sensor. In other words, the force attenuator can significantly extend the maximum sensing range of a given force sensor.

[0033] Referring now to FIG. 1, a force attenuator 101 is shown. The force attenuator 101 includes a deformable slab 105 with a plurality (e.g. two) opposing surfaces 105A, 105B. In some implementations, surfaces 105A, 1056 are parallel, which can help reduce preload on a force sensor. The deformable slab 105 has a cylindrical shape such that each of the opposing surfaces 105A, 105B has a circular cross section as shown in FIG. 1. It should be understood that the deformable slab having a cylindrical shape is provided only as an example. This disclosure contemplates that the deformable slab can have other shapes. In some implementations, the deformable slab 105 is formed of a rubber material. It should be understood that rubber material is provided only as an example. This disclosure contemplates that the deformable slab 105 can be made of other deformable materials including, but not limited to, elastomers, silicone rubber, polyurethane, acrylonitrile butadiene styrene (ABS), or a material with a Young's modulus less than about 2 gigapascals (GPa) that can tolerate a strain larger than about 10% without yielding. In FIG. 1, the force is applied to a top surface 103 of the force attenuator 101. Additionally, the force attenuator 101 can define a surface area for receiving an applied force, for example, the surface area of the top surface 103. In some implementations, surface 105A can serve as the top surface of the force attenuator 101 (not shown). In other implementations, a surface of a non-deformable slab, which is described in detail below, can serve as the top surface of the force attenuator 101 as shown in FIG. 1. It should be understood that the force sensor itself can define a surface area for receiving an applied force, which is transferred through the force attenuator 101.

[0034] The force attenuator 101 can include a cavity 102. The dimensions (e.g., size and/or shape) of the cavity 102 can be designed to accommodate a force sensor. In other words, the force sensor can be arranged or placed inside of the cavity 102. In some implementations, the force sensor can be fitted inside the cavity 102. In this way, the force that is applied to the force attenuator 101 is transferred to the force sensor. Optionally, the force sensor can be a MEMS force sensor as described herein. Example MEMS force sensors are described in U.S. Pat. No. 9,487,388, issued Nov. 8, 2016 and entitled Ruggedized MEMS Force Die; U.S. Pat. No. 9,493,342, issued Nov. 15, 2016 and entitled Wafer Level MEMS Force Dies; U.S. Pat. No. 9,902,611, issued Feb. 27, 2018 and entitled Miniaturized and ruggedized wafer level mems force sensors; U.S. Patent Application Publication No. 2016/0363490 to Campbell et al., filed Jun. 10, 2016 and entitled Ruggedized wafer level mems force sensor with a tolerance trench; WO2018/148503 to NextInput, Inc., filed Feb. 9, 2018 and entitled INTEGRATED DIGITAL FORCE SENSORS AND RELATED METHODS OF MANUFACTURE; and WO2018/148510 to NextInput, Inc., filed Feb. 9, 2018 and entitled INTEGRATED PIEZORESISTIVE AND PIEZOELECTRIC FUSION FORCE SENSOR, the disclosures of which are incorporated by reference in their entireties. As shown in FIG. 1, the cavity 102 is formed on a bottom surface 107 of the force attenuator 101. For example, the cavity 102 is formed on surface 105B of the deformable slab 105. The force sensor can be fitted inside the cavity 102 such that it receives the force applied on the top surface 103 of the force attenuator 101. As described above, the force sensor can define a surface area, which is smaller than the surface area of the force attenuator 101. For example, the surface area of the surface of a MEMS force sensor that receives the applied force is typically on the order of mm.sup.2. The surface area of the surface of the force attenuator (e.g., top surface 103 shown in FIG. 1) that receives the applied force can be orders of magnitude larger than that of the force sensor. As described below, the ratio of the force sensor's surface area to the force attenuator's surface area has a linear relationship to sensitivity attenuation (see FIG. 5). Additionally, a depth of the cavity (also referred to herein as cavity depth), which is shown by opposing arrows 104 in FIG. 1, is designed such that a height of the force sensor is equal to, or slightly larger than, the cavity depth 104. A thickness of the deformable slab 105, which is shown by opposing arrows 108 in FIG. 1, is designed such that there is still sufficient material (e.g., rubber) disposed over the force sensor at maximum load. For example, a typical force sensor has a height in the range of about 0.2 mm-0.6 mm. Accordingly, in some implementations, the cavity depth 104 can be equal to the height of the force sensor (e.g., about 0.2 mm-0.6 mm depending on the force sensor). Alternatively, in other implementations, the cavity depth 104 can be about 25 micrometers (m)-50 m less than the height of the force sensor, which ensures that the force attenuator 101 contacts the force sensor but without applying excessive preload to the force sensor.

[0035] Optionally, the force attenuator 101 can be in the shape of a stacked slab. For example, the force attenuator 101 can optionally further include a solid non-deformable slab 106 disposed on top of the deformable slab 105, e.g., forming the stacked slab as shown in FIG. 1. The solid non-deformable slab 106 can have a size and/or shape that matches the size and/or shape of the deformable slab 105 in cross section. For example, the solid non-deformable slab 106 shown in FIG. 1 has a cylindrical shape. It should be understood that the solid non-deformable slab having a cylindrical shape is provided only as an example. This disclosure contemplates that the solid non-deformable slab can have other shapes. This disclosure contemplates that the solid non-deformable slab 106 can be made of a non-deformable material. The solid non-deformable slab 106 can evenly distribute the force load applied on the top surface 103 of the force attenuator 101. The solid non-deformable slab 106 can be provided when there is a risk of damage to the force sensor.

[0036] Referring now to FIG. 2, an example force attenuated force sensor is described. In FIG. 2, the force sensor system 201 (e.g., the force attenuated force sensor) includes a force attenuator (e.g., the force attenuator 101 shown in FIG. 1) and a force sensor 202. The force attenuator includes a deformable slab 105 and a solid non-deformable slab 106. A cavity 102 is provided in the deformable slab 105, and the force sensor 202 is arranged inside the cavity 102. The force attenuator is described in detail above with regard to FIG. 1 and is therefore not described in further detail below with regard to FIG. 2. As described below, the force sensor 202 can include a piezoresistive sensing element.

[0037] As described above, the force sensor system 201 can include the force sensor 202. The force sensor system 201 can also include a package substrate 208 such as a printed circuit board (PCB) or a flexible printed circuit board (FPC). The force sensor 202 and the package substrate 208 can be arranged in the cavity 102 of the force attenuator. The force sensor 202 can include a dielectric layer 203, a sensor substrate 204 (e.g., a sensor die), and a piezoresistive sensing element 205. In some implementations, the force sensor 202 can include a plurality of piezoresistive sensing elements 205. This disclosure contemplates that the piezoresistive sensing element(s) 205 can be diffused, deposited, or implanted on a surface of the force sensor 202. The force sensor 202 can also include a metal layer 206 and a solder bump 207. The metal layer 206 and solder bump 207 can be used to electrically and mechanically connect the force sensor 202 to the package substrate 208. Additionally, as shown in FIG. 2, the force attenuator and the package substrate 208 can be mechanically coupled to a solid surface 210 to provide reaction force. An example MEMS force sensor including a piezoresistive sensing element is described in PCT application No. PCT/US2018/056245 to NextInput, Inc., filed Oct. 17, 2018 and entitled INTEGRATED PIEZORESISTIVE AND PIEZOELECTRIC FUSION FORCE SENSOR, the disclosure of which is incorporated by reference in its entirety.

[0038] Referring now to FIG. 3, another example force attenuated force sensor is described. In FIG. 3, the force sensor system 301 (e.g., the force attenuated force sensor) includes a force attenuator (e.g., the force attenuator 101 shown in FIG. 1) and a force sensor 202. The force attenuator includes a deformable slab 105 and a solid non-deformable slab 106. A cavity 102 is provided in the deformable slab 105, and the force sensor 202 is arranged inside the cavity 102. The force attenuator is described in detail above with regard to FIG. 1 and is therefore not described in further detail below with regard to FIG. 3. As described below, the force sensor 202 can include both piezoresistive and piezoelectric sensing elements.

[0039] As described above, the force sensor system 301 can include the force sensor 202. The force sensor system 301 can also include a package substrate 208 such as a PCB or an FPC. The force sensor 202 and the package substrate 208 can be arranged in the cavity 102 of the force attenuator. The force sensor 202 can include a dielectric layer 203, a sensor substrate 204 (e.g., a sensor die), and a piezoresistive sensing element 205. In some implementations, the force sensor 202 can include a plurality of piezoresistive sensing elements 205. This disclosure contemplates that the piezoresistive sensing element(s) 205 can be diffused, deposited, or implanted on a surface of the force sensor 202. Additionally, the force sensor 202 can include a piezoelectric sensor. A piezoelectric sensor can include a piezoelectric sensing element 312 arranged between opposing electrodes. In FIG. 3, the piezoelectric sensing element 312 is sandwiched between piezoelectric electrode 313 and metal layer 206 (e.g., the opposing electrodes). Piezoresistive and piezoelectric sensing elements can be used together in MEMS force sensors. For example, piezoresistive sensing elements are useful for sensing static forces applied to the force sensor 202, while piezoelectric sensing elements are useful for sensing dynamic forces acting on the force sensor 202. Thus, both piezoresistive and piezoelectric sensors can be used in conjunction to detect both static and dynamic forces. The force sensor 202 can also include a metal layer 206 and a solder bump 207. The metal layer 206 and solder bump 207 can be used to electrically and mechanically connect the force sensor 202 to the package substrate 208. Additionally, as shown in FIG. 3, the force attenuator and the package substrate 208 can be mechanically coupled to a solid surface 210 to provide reaction force. An example MEMS force sensor including both piezoresistive and piezoelectric sensing elements is described in PCT application No. PCT/US2018/056245 to NextInput, Inc., filed Oct. 17, 2018 and entitled INTEGRATED PIEZORESISTIVE AND PIEZOELECTRIC FUSION FORCE SENSOR, the disclosure of which is incorporated by reference in its entirety.

[0040] Referring now to FIG. 4, yet another example force attenuated force sensor is described. In FIG. 4, the force sensor system 401 (e.g., the force attenuated force sensor) includes a force attenuator (e.g., the force attenuator 101 shown in FIG. 1) and a force sensor 402. The force attenuator includes a deformable slab 105 and a solid non-deformable slab 106. A cavity 102 is provided in the deformable slab 105, and the force sensor 402 is arranged inside the cavity 102. The force attenuator is described in detail above with regard to FIG. 1 and is therefore not described in further detail below with regard to FIG. 4. As described below, the force sensor 402 can include a sealed cavity.

[0041] As described above, the force sensor system 401 can include the force sensor 402. The force sensor system 401 can also include a package substrate 410 such as a PCB or an FPC. The force sensor 402 and the package substrate 410 can be arranged in the cavity 102 of the force attenuator. The force sensor 402 can include a dielectric layer 403, a sensor substrate 404 (e.g., a sensor die), and a piezoresistive sensing element 405. In some implementations, the force sensor 402 can include a plurality of piezoresistive sensing elements 405. This disclosure contemplates that the piezoresistive sensing element(s) 405 can be diffused, deposited, or implanted on a surface of the force sensor 402. Optionally, in some implementations, the force sensor 402 can include piezoelectric sensing element(s). The force sensor 402 can also include a cap substrate 408, which is attached to the sensor substrate 404 through a bonded oxide layer 407. The internal surfaces between the sensor substrate 404 and the cap substrate 408 form a sealed cavity 450. The sealed cavity 450 can be formed by etching a trench from the sensor substrate 404 and then sealing a volume between the bonded sensor substrate 404 and cap substrate 408. For example, the volume is sealed between the sensor substrate 404 and the cap substrate 408 when adhered together, which results in formation of the sealed cavity 450. The force sensor 202 can also include a metal layer 406 and a solder bump 409. The metal layer 406 and solder bump 409 can be used to electrically and mechanically connect the force sensor 402 to the package substrate 410. Additionally, as shown in FIG. 4, the force attenuator and the package substrate 410 can be mechanically coupled to a solid surface 412 to provide reaction force. An example MEMS force sensor including a sealed cavity is described in U.S. Pat. No. 9,902,611, issued Feb. 27, 2018 and entitled Miniaturized and ruggedized wafer level mems force sensors; U.S. Patent Application Publication No. 2016/0363490 to Campbell et al., filed Jun. 10, 2016 and entitled Ruggedized wafer level mems force sensor with a tolerance trench; and PCT application No. PCT/US2018/056245 to NextInput, Inc., filed Oct. 17, 2018 and entitled INTEGRATED PIEZORESISTIVE AND PIEZOELECTRIC FUSION FORCE SENSOR, the disclosures of which are incorporated by reference in their entireties.

[0042] Referring now to FIG. 5, a graph illustrating the relationship of sensitivity attenuation and the area ratio between the force attenuator and force sensor is described. In FIG. 5, sensitivity attenuation is on the y-axis, and area ratio is on the x-axis. As described herein, the area ratio is the ratio of the respective surface areas of the force-receiving surfaces of the force attenuator and the force sensor. It should be understood from FIG. 5 that the area ratio between the surface area of the top surface of a force attenuator and the surface area of the top surface of a force sensor affects sensitivity attenuation. For example, by changing the area of the top surface of the force attenuator (e.g., top surface 103 of the force attenuator 101 shown in FIG. 1) and keeping the area of the top surface of a sensor (e.g., force sensor 202 or 402 shown in FIGS. 2-4) the same, it is possible to simulate the sensitivity from the force sensor caused by the force applied on the top surface of the attenuator. It is observed from FIG. 5 that from the sensor surface area versus the force attenuator surface area ratio from 1:1000 to 1:10, the relationship between sensitivity attenuation and area ratio is linear. This indicates that the maximum load from the combination of the force attenuator and the force sensor is effectively increased by a factor of 1000 in a linear fashion. This is an efficient solution to increase the maximum load of the force sensor.

[0043] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.