Flexible apparatus and method to enhance capacitive force sensing

A flexible apparatus and method to enhance capacitive force sensing is disclosed. In one embodiment, a force measuring device includes a sensor capacitor having a fixed surface and a movable surface substantially parallel to the fixed surface, at least one spring assembly (e.g., may deflect longitudinally and/or perpendicularly to a direction of the force) positioned between the fixed surface and the movable surface (e.g., the spring assembly may alter in height in response to a force applied perpendicular to the movable surface and to cause a change in the gap between the fixed surface and the movable surface), and a circuit to generate a measurement of the force based on an algorithm that considers a change in a capacitance of the sensor capacitor. A reference capacitor may adjust the measurement of the applied force based on one or more environmental conditions.

CLAIM OF PRIORITY

FIELD OF TECHNOLOGY

This disclosure relates generally to the technical fields of measuring devices and, in one embodiment, to gap-change sensing through capacitive techniques.

BACKGROUND

A load cell may be a device (e.g., a transducer) that converts a force to a differential signal (e.g., a differential electric signal). The load cell may be used for a variety of industrial applications (e.g., a scale, a truck weigh station, a tension measuring system, a force measurement system, a load measurement system, etc.) The load cell may be created using a strain gauge. The strain gauge can be used to measure deformation (e.g., strain) of an object. The strain gauge may include a flexible backing which supports a metallic foil pattern etched onto the flexible backing. As the object is deformed, the metallic foil pattern is deformed, causing its electrical resistance to change.

The strain gauge can be connected with other strain gauges to form a load cell in a Wheatstone-bridge configuration (e.g., constructed from four strain gauges, one of which has an unknown value, one of which is variable, and two of which are fixed and equal, connected as the sides of a square). When an input voltage is applied to the load cell in the Wheatstone-bridge configuration, an output may become a voltage proportional to the force on the load cell. The output may require amplification (e.g., 125×) by an amplifier before it can be read by a user (e.g., because the raw output of the Wheatstone-bridge configuration may only be a few milli-volts). In addition, the load cell in the Wheatstone-bridge configuration may consume a significant amount of power when in operation (e.g., in milli-watts of power).

Manufacturing the load cell in the Wheatstone-bridge configuration may involve a series of operations (e.g., precision machining, attaching strain gauges, match strain gauges, environmental protection techniques, and/or temperature compensation in signal conditioning circuitry, etc.). These operations may add complexity that may deliver a yield rate of only 60%, and may allow a particular design of the load cell to only operate for a limited range (e.g., between 10-5,000 lbs.) of measurement. In addition, constraints of the Wheatstone-bridge configuration may permit only a limited number of form factors (e.g., an s-type form factor and/or a single point form factor, etc.) to achieve desired properties of the load cell. The complexity of various operations to manufacture and use load cell may drive costs up (e.g., hundreds and thousands of dollars) for many industrial applications.

Conventional capacitive force sensing devices suffer from several constraints of the springs which are used in such devices. Some of these constraints are relaxation and/or creep, hysteresis, set, and off-axis loading. Particularly, hysteresis is a limitation inherent to the use of various springs (e.g, lagging of an effect behind its cause). When there is a difference in spring deflection at the same applied load—during loading and/or unloading—the spring may have hysteresis. Hysteresis could result from set, creep, relaxation and/or friction. Hysteresis may limit the usefulness of a capacitive force sensing device. Specifically, the spring may consistently and repeatedly return to its original position as the load is applied and/or removed. Failure to do so may cause erroneous readings.

An off-axis loading may occur when the direction of an applied load is not along a normal axis of a sensor. The off-axis loading can cause the surfaces to become non-parallel and/or can significantly impact various measurements. Many traditional springs such as helical springs or elastomeric springs (made from polymers, e.g., rubber or plastic) may suffer from many of the above constraints and consequently may not be suitable for high precision applications.

SUMMARY

A flexible apparatus and method to enhance capacitive force sensing is disclosed. In one aspect, a force measuring device includes a sensor capacitor having a fixed surface and a movable surface substantially parallel to the fixed surface, at least one spring assembly positioned between the fixed surface and the movable surface (e.g., may alter in height in response to a force applied perpendicular to the movable surface and to cause a change in a gap between the fixed surface and the movable surface), and a circuit to generate a measurement of the force based on an algorithm that considers a change in a capacitance of the sensor capacitor.

The force measuring device may include a reference capacitor to adjust the measurement based on one or more environmental conditions. A shielding spacer may be placed between the reference capacitor and a bottom layer to minimize an effect of a stray capacitance affecting the measurement. One or more spring assemblies may deflect longitudinally and/or perpendicularly to a direction of the force such that a perpendicular deflection does not contact the movable surface and the fixed surface.

The spring assemblies may be formed by a conical washer having an inside edge of the conical washer that is wider than an outside edge of the conical washer. The conical washer may be stacked with other conical washers to form the at least one spring assembly. The fixed surface and/or the movable surface may be painted on any number of non-conductive printed circuit boards.

In another aspect, a force measuring device includes a sensor capacitor having a fixed surface and a movable surface substantially parallel to the fixed surface, a fixed layer perpendicular to the movable surface, at least one spring assembly positioned between the movable surface and/or the fixed layer to alter in height in response to a force applied parallel to the movable surface (e.g., and to cause a change in an overlap area between the fixed surface and the movable surface), and a circuit to determine a measurement based on an algorithm that considers a change in capacitance when the overlap area changes. A reference capacitor may be integrated in the force measuring device to adjust based on one or more environmental conditions between the fixed surface and another fixed surface.

In yet another aspect, a method to measure force includes positioning at least one spring assembly between a fixed surface and a movable surface, applying a force (e.g., a load, a stress, etc.) perpendicular to the movable surface to cause a change in the height of the at least one spring assembly and to cause a change in a gap between the fixed surface and the movable surface, and automatically generating a measurement of a force based on an algorithm that considers a change in a capacitance between the fixed surface and the movable surface. The measurement of the force may be adjusted based on a change in a reference capacitance that is affected primarily because of one or more environmental conditions.

In a further aspect, a system (e.g., and/or method) to measure force may include positioning an elastic device between a movable surface and a fixed surface perpendicular to the movable surface, causing the elastic device to change form based on a force applied adjacent to the movable surface, and automatically generating a measurement of the force based on a change in an overlap area between a fixed surface and the movable surface. In addition the system may include forming the reference capacitor by substantially parallel plates of the fixed surface and a reference surface, and adjusting the measurement based on a change in capacitance of a reference capacitor whose capacitance changes primarily because of one or more environmental conditions. The methods, systems, and apparatuses disclosed herein may be implemented in any means for achieving various aspects, and may be executed in a form of a machine-readable medium embodying a set of instructions that, when executed by a machine, cause the machine to perform any of the operations disclosed herein. Other features will be apparent from the accompanying drawings and from the detailed description that follows.

DETAILED DESCRIPTION

Example embodiments, as described below, may be used to provide high-accuracy, low-cost, force sensing devices (e.g., load sensors, pressure sensors, etc.). It will be appreciated that the various embodiments discussed herein may/may not be the same embodiment, and may be grouped into various other embodiments not explicitly disclosed herein. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. It will be evident, however, to one skilled in the art that the various embodiments may be practiced without these specific details.

A spring assembly which overcomes the problems of relaxation, creep, hysteresis, set, and/or off-axis loading is disclosed in one embodiment. The spring assembly in its various embodiments has the property that when a force is applied to the spring assembly, the spring assembly deflects both longitudinally (e.g., along a direction of an applied force) and perpendicularly to a direction of the applied force. However, at the points where the spring assembly contacts other surfaces and/or layers, a perpendicular deflection is negligible which reduces the problem of friction and, therefore, hysteresis.

The various embodiments of the spring assembly may be used in different types of force measuring devices (e.g., a gap-change sensing device, an area-change sensing device, etc.). The spring assembly may include a conical metal washer. The metal conical washer may provide several substantial advantages. The metal conical washer may have a large base (e.g., 3×) compared to its height combined with a large flat top surface which makes it unlikely that the applied force will cause the movable surface to suffer off-axis loading thus becoming non-parallel. Further, metals may be less susceptible to set and creep than other materials.

In another embodiment of the spring assembly, the spring assembly may include two conical washers placed back to back in such a way that the top and/or bottom surfaces are wide, but not as wide as the middle. In another embodiment, the spring assembly may include multiple pairs of conical washers placed back to back. In yet another embodiment of the spring assembly, the spring assembly includes multiple sets of conical metal washers placed base to base, each set including at least one conical metal washer.

The various embodiments of the spring assembly may be used in different types of force measuring devices (e.g., a gap-change sensing device, an area-change sensing device, etc.). In a gap-change sensing device, the spring assembly can be positioned between a fixed surface and a movable surface which is substantially parallel to the fixed surface. When a force is applied perpendicular to the movable surface, the height of the spring assembly may be changed and this may cause change in the gap between the fixed surface and the movable surface. The change in the gap between the fixed surface and the movable surface may cause a change in the capacitance between the fixed surface and the movable surface, which can algorithmically be measured as a force.

In an area-change sensing device, a sensor capacitor may have a fixed surface and a movable surface substantially parallel to the fixed surface, a fixed layer perpendicular to the fixed surface, and at least one spring assembly positioned between the movable surface and the fixed layer to alter in height in response to a force applied adjacent to the movable surface, and to cause a change in an overlap area between the fixed surface and the movable surface, and a circuit to determine a measurement based on an algorithm that considers a change in capacitance when the overlap area changes.

A spring assembly as disclosed in the various embodiments herein can overcome the problems of relaxation, creep, hysteresis, set, and/or off-axis loading which are prevalent in conventional springs used in different force measuring devices through the use of flexible devices having elastic qualities (e.g., spring assemblies, devices100,200,300,400ofFIGS. 1-4, etc.). The spring assemblies in their various embodiments may have the property that when a force is applied to the spring assembly, the spring assembly may deflect both longitudinally (along the direction of the applied force) and perpendicularly to the direction of the applied force. However, at the points where the spring assembly contacts other surfaces and/or layers, the perpendicular deflection may be negligible which reduces the problem of friction and, therefore, hysteresis.

A few embodiments of spring assembly have been shown inFIGS. 1-4by way of illustration. The various embodiments of the spring assembly may be used in different types of force measuring devices (including, e.g., a gap-change sensing device, an area-change sensing device, etc.).

FIG. 1is a cross-sectional view of a device100, with a conical washer140positioned between a fixed surface170and a movable surface110, and exhibiting a deflection in response to an applied force105, according to one embodiment. The conical washer140may have an inside edge that is wider than an outside edge, and may be made of metal (e.g., metals may be less susceptible to set and creep than other materials). In alternate embodiments, the conical washer140may be created from a synthetic material (e.g., a polymer based material). The conical washer140may deflect both longitudinally120(along the axis) and perpendicularly160(perpendicular to the axis) to the direction of unknown force105. When the force105is applied to the conical metal washer140, the movable surface110shifts to the position150.

At the points where the conical metal washer is in contact with other surfaces and/or layers (e.g., the movable surface110), a perpendicular deflection (e.g., perpendicular to the direction of the force105) may be negligible. This may reduce friction and, therefore, hysteresis. The fixed surface170and the movable surface110may be painted (e.g., sputtered, coated) on multiple non-conductive printed circuit boards (e.g., the printed circuit boards502,506,510ofFIG. 5). The conical metal washer140may have a large base compared to its height. In addition, a large flat top surface may make it unlikely that the applied force will cause off-axis loading.

FIG. 2is a cross-sectional view of a device200, with two metal conical washers positioned back to back between the fixed surface170and the movable surface110, according to one embodiment. A first conical washer230and a second conical washer260may be placed back to back in such a way that the top and bottom surfaces are wide, but not as wide as the middle. As a force105is applied against the movable surface110, it may cause a longitudinal deflection220in the device200, and perpendicular deflections270and280in the conical washers230and260. However, at the points where the conical washer230contacts the movable surface110and where the conical washer260contacts the fixed surface170, perpendicular deflections240and250are negligible, which may reduce the problem of friction and therefore, hysteresis. The conical washers230and260may be bonded together using an adhesive and/or glue in one embodiment. In alternate embodiments, the conical washers230and260may be welded together.

FIG. 3is a cross-sectional view of a device300, with multiple metal conical washers positioned back to back between the fixed surface170and the movable surface110, according to one embodiment. As the force105, also shown inFIG. 1, is applied against the movable surface110, it causes longitudinal deflection320in the spring assembly, and perpendicular deflections in conical washers330,340,350, and360. However, at the points where the conical washer330contacts the movable surface110, where the conical washer360contacts the fixed surface170, and also where the conical washer340contacts conical washer350, perpendicular deflections may be negligible. The

FIG. 4is a cross-sectional view of a device400, with multiple sets of multiple metal conical washers positioned back to back between the fixed surface and the movable surface, according to one embodiment.FIG. 4illustrates a device400in which multiple sets (e.g., one set may have two washers) of conical washers are placed base to base (e.g., back to back), each set including at least one conical metal washer. As the force105, also shown inFIG. 1, is applied against the movable surface110, it may cause longitudinal deflection420in the device400, and perpendicular deflections in all the conical washers, similar to the perpendicular deflections shown inFIGS. 2 and 3. The device300ofFIG. 3and the device400ofFIG. 4illustrate different configurations of the device200ofFIG. 2that may be employed to provide further advantages in various applications (e.g., higher load measurement capacity, lesser likelihood of off-axis loading).

In a gap-change sensing device, a spring assembly (e.g., the assembly of conical washers330,340,350, and360ofFIG. 3) may be positioned between a fixed surface (e.g., the fixed surface170ofFIG. 1) and a movable surface (e.g., the movable surface110ofFIG. 1) that is substantially parallel to the fixed surface. When a force is applied perpendicular to the movable surface, it causes change in the gap between the fixed surface and the movable surface. The change in the gap between the fixed surface and the movable surface may cause a change in the capacitance between the fixed surface and the movable surface. A gap-change sensing device may generate a measurement based on the change in capacitance of a sensor capacitor resulting from a change in a gap between a fixed surface and a movable surface. A reference capacitor may be used to adjust the measurement based on at least one environmental condition.

FIG. 5is a three-dimensional view of a stacked device550having a sensor capacitor (e.g. formed by the fixed surface170and the movable surface110ofFIG. 1) and a reference capacitor (e.g., formed by the surface622ofFIG. 6Cand the surface628ofFIG. 6E), according to one embodiment. The stacked device550ofFIG. 5includes a top layer500, a printed circuit board502, a device504(e.g., the devices100,200,300,400), a printed circuit board506, a spacer508, a printed circuit board510, a shielding spacer512, and a bottom layer514. A cable516(e.g., an interface cable) may connect the stacked device550to a data processing system. In addition, a force518(e.g., a load, a weight, a pressure, etc.) may be applied to the top layer500. The various components of the stacked device550are best understood with reference toFIG. 6A-6G.

FIGS. 6A-6Gare exploded views of the stacked device550ofFIG. 5.FIG. 6Aillustrates the top layer500and the printed circuit board502. The top layer500may be created from a material such as aluminum, steel, and/or a plastic, etc. The printed circuit board502includes a surface616. The surface616may be painted (e.g., sputtered, coated, etc.) on the printed circuit board502. The printed circuit board502may be coupled (e.g., screwed onto, bonded, etched, glued, affixed, etc.) to the top layer500as illustrated inFIG. 6Aso that when the force518(e.g., as illustrated inFIG. 5) is applied to the top layer500, the height of the spring assembly504(e.g., as illustrated inFIG. 5) is reduced, resulting in change in the gap between the surface616and a surface620separated by the spring assembly504as illustrated inFIG. 6B.

FIG. 6Cis a view of the printed circuit board506(e.g., a non-conductive material). In the embodiment illustrated inFIG. 6C, a surface620(e.g., a conductive surface) is painted (e.g., coated, sputtered, etc.) on the printed circuit board506on one side. In addition, a surface622may be painted on the other side of the printed circuit board506as illustrated inFIG. 6C. The surface616may be painted (e.g., sputtered, coated, etc.) on the printed circuit board506. The change in the gap between the surface616and the surface620may cause a change in capacitance of a sensor capacitor (e.g., the sensor capacitor formed by the surface616and the surface620separated by the spring assembly504.

In one embodiment, the surface616and the surface620are substantially parallel to each other and have the same physical area and/or thickness. A change in capacitance of the sensor capacitor may be inversely proportional to the change in the distance between the surface616and the surface620in one embodiment.

The spring assembly504ofFIG. 6Cmay be coated with an insulating material at the ends where it comes in contact with the fixed surface620and the movable surface616(e.g., to avoid a short circuit). In one embodiment, the spring assembly504may be created from a conductive synthetic material rather than solely one or more metals. The spring assembly504may create a gap between the surface616and the surface620. The gap can be filled with air or any other gas (e.g., an inert gas).

The surface622as illustrated inFIG. 6Cand the surface628as illustrated inFIG. 6Emay be separated by the spacer508as illustrated inFIG. 6D. The surface622and the surface628may form a reference capacitor according to one embodiment. Since the surface622and the surface628may not alter positions with respect to each other when the force518is applied to the top layer500, their capacitance may not change (e.g., capacitance is calculated as “capacitance=(dielectric constant multiplied by area of overlap) divided by (distance between surfaces)”) in response to the applied force518.

As such, the reference capacitor formed by the surface622and the surface628may experience a change in capacitance only for environmental factors (e.g., humidity in a gap between the first surface and the second surface, a temperature of the stacked device550, and an air pressure of an environment surrounding the stacked device550, etc.). Therefore, the effect of these environmental conditions can be removed from a measurement of a change in capacitance of the sensor capacitor (e.g. formed by the surface616and the surface620) when the force518is applied to the stacked device550to more accurately determine a change in capacitance of the sensor capacitor.

A processing module624as illustrated inFIG. 6Eof the stacked device550may be used to generate a measurement based on a change in a distance between the surface616ofFIG. 6Aand the surface620ofFIG. 6C(e.g., through coupling the stacked device550through a connector624ofFIG. 6Ewith the cable512ofFIG. 5). In addition, the processing module624may generate a measurement of the sensor capacitor after removing an effect of the environmental condition from a capacitance of the sensor capacitor (e.g., by subtracting the changes in the reference capacitor, which may be only affected by environmental conditions).

The shielding spacer512as illustrated inFIG. 6Fmay separate the printed circuit board510from a bottom layer514(e.g., to minimize an effect of a stray capacitance affecting the measurement). The bottom layer514is illustrated inFIG. 6G. The various components illustrated inFIGS. 6A-6Gmay physically connect to each other to form the stacked device550in one embodiment (e.g., in alternate embodiments the various components may be screwed together, welded together, bound together, etc.).

The spring assembly504of the stacked device550ofFIG. 5in different embodiments may include one or more metal conical washers. According to one embodiment, the spring assembly504of the stacked device550may include one conical washer, as illustrated inFIG. 1. According to another embodiment, the spring assembly504of the stacked device550may include a pair of conical washers, as illustrated inFIG. 2. According to another embodiment, the spring assembly504of the stacked device550may include multiple pairs of conical washers stacked on top of each other, as illustrated inFIG. 3. According to yet another embodiment, the spring assembly504of the stacked device550may include multiple sets of conical washers, each set including at least one conical washer, as illustrated inFIG. 4.

FIG. 7is an area-sensing device750formed by two substantially parallel surfaces and a spring assembly positioned between the movable surface and a fixed layer, according to one embodiment. Device750includes a top layer702(e.g., a conductive and/or non-conductive substrate) and a bottom layer704(e.g., a conductive and/or non-conductive substrate), according to one embodiment. A force700is applied to the top layer702inFIG. 7. The top layer702includes a movable surface706perpendicular to the top layer702. The bottom layer704includes a surface708and a surface710, both the surfaces perpendicular to the bottom layer704.

The movable surface706is substantially perpendicular to the fixed layer704, but is not directly in contact with the fixed layer, the device504being positioned between the movable surface706and the fixed layer704(e.g., illustrated as encompassed by a rectangular non-conductive material that can flex, such as a polymer based material). The surface706and the surface708(e.g., the surface706and the surface708may be substantially parallel to each other) form a sensor capacitor714(e.g., the sensor capacitor714may be a variable capacitor formed because two conductive surfaces/plates are separated and/or insulated from each other by an air dielectric between the surface706and the surface708) in an area that overlaps the surface706and the surface708. The surface706may be movable relative to the surface708in one embodiment. In addition, a reference capacitor712is formed between the surface708and the surface710(e.g., a reference surface). The surface710may be substantially parallel to the surface706and/or with the surface708in one embodiment. In addition, the surface710may be electrically coupled to the surface706and/or the surface708. Since the surface708and the surface710may not alter positions with respect to each other when the force700is applied to the top layer710, their capacitance may not change.

The spring assembly504of the area-sensing device750ofFIG. 7in different embodiments may include one or more metal conical washers. According to one embodiment, the spring assembly504of the area-sensing device750may include one conical washer, as illustrated inFIG. 1. According to another embodiment, the spring assembly504of the area-sensing device750may include a pair of conical washers, as illustrated inFIG. 2. According to another embodiment, the spring assembly504of the area-sensing device750may include multiple pairs of conical washers stacked on top of each other, as illustrated inFIG. 3. According to yet another embodiment, the spring assembly504of the area-sensing device750may include multiple sets of conical washers, each set including at least one conical washer, as illustrated inFIG. 4

FIG. 8is a multi-depth device850according to one embodiment. InFIG. 8, a top layer702, a middle layer704, and a bottom layer814are illustrated. The top layer702includes a plate706(e.g., a conductive surface). The plate706may be electrically separated from the top layer702by application of an insulating material between an area of affixation between the top layer702and the plate706. A force700may be applied to the top layer702and the plate706to cause the plate706to deflect (e.g., move inward once a load and/or force700is applied to the top layer702as illustrated inFIG. 8). The movable surface706is substantially perpendicular to the fixed layer704, but is not directly in contact with the fixed layer, the device504being positioned between the movable surface702and the fixed layer704.

The middle layer704includes a plate708and the plate810. In one embodiment, the middle layer804may include two separate layers bonded together each having either the plate708or the plate810. The bottom layer814includes a plate816. In one embodiment, there may be a shielding spacer (e.g., not shown, but the shielding spacer may be any type of spacer) between the reference capacitor (e.g., formed by the plate810and the plate816) and a bottom of the housing (e.g., the bottom layer814) to minimize an effect of a stray capacitance affecting the measurement (e.g., a height of the shielding spacer may be at least ten times larger than a plate spacer between plates of the reference capacitor and between plates of the sensor capacitor in one embodiment to minimize the stray capacitance). The plate806and the plate808may form a sensor capacitor (e.g., as formed by the fixed surface170and the movable surface110ofFIG. 1). Similarly, the plate810and the plate816may form a reference capacitor (e.g., as formed by the plate810and the plate816).

A spacer811may be used to physically separate the top layer802from the middle layer804. In one embodiment, the spring assembly504(e.g., conical back to back springs) may be placed between (e.g., in the outer periphery between) the top plate702ofFIG. 8and the housing811ofFIG. 8. A spacer812may be used to physically separate the middle layer804from the bottom layer814. The multi-depth device850may be easier to manufacture according to one embodiment because of modularity of its design (e.g., various manufacturing techniques can be used to scale the multi-depth device850with a minimum number of sub-assemblies) in that various sub-assemblies may each include only one surface (e.g., the top layer802, the middle layer804, and the bottom layer816may include only one plate).

FIG. 9is a process view to automatically generate a measurement based on a change in a gap and/or a change in an overlap area between a fixed surface and a movable surface, according to one embodiment.FIG. 9is a process view of measuring a force900, according to one embodiment. InFIG. 9, a force900may be applied to a sensor902(e.g., the applied force518ofFIG. 5, or the applied force700ofFIG. 7), according to one embodiment. An electronic circuitry (e.g., a software and/or hardware code) may apply an algorithm to measure a change in a distance between the surface616and the surface620forming the sensor capacitor as illustrated inFIG. 6AandFIG. 6C(e.g., the sensor902may include the spring assembly504ofFIG. 5and/or any one or more of the devices100,200,300, and400ofFIGS. 1-4) when the force518ofFIG. 5is applied to a device (e.g., the stacked device550). In an alternate embodiment, a change in area between the surfaces may be considered rather than a change in the gap (e.g., the change in an overlap area between the surface706and the surface708forming the sensor capacitor as illustrated inFIG. 7).

Next, a change in capacitance906may be calculated based on the change in the gap between the surfaces forming the sensor capacitor or change in the overlap area between the surfaces forming the sensor capacitor. The change in capacitance906, a change in a voltage908, and/or a change in a frequency910may also be calculated to generate a measurement (e.g., an estimation of the force900applied to the sensor902). The change in capacitance906data, the change in voltage908data, and/or the change in frequency data910may be provided to a digitizer module912(e.g., an analog-to-digital converter). Finally, the digitizer module912may work with a processing module914(e.g., a microprocessor which may be integrated in the processing module224) to convert the change in capacitance906data, the change in voltage908data, and/or the change in frequency data910to a measurement reading916.

FIG. 10is a three-dimensional view of a carved material that can be used to encompass (e.g., provide a housing to) the sensor capacitor (e.g., the sensor capacitor714as illustrated inFIG. 7and the reference capacitor (e.g., the reference capacitor712illustrated inFIG. 7) in a boxed device, according to one embodiment. InFIG. 10, single block (e.g., steel) is used to form a bottom cup1014. In one embodiment, the bottom cup1014inFIG. 10replaces the bottom layer of a boxed device, and encompasses the various structures (e.g., capacitive surfaces/plates, spacers, etc.) between a bottom layer and a top plate. The bottom cup1014may be formed from a single piece of metal through any process (e.g., involving cutting, milling, etching, and/or drilling, etc.) that maintains the structural and/or tensile integrity of the bottom cup1014. This way, the bottom cup1014may be able to withstand larger amounts of force (e.g., the force105ofFIG. 1) by channeling the force downward through the walls of the bottom cup1014.

FIG. 11is a three-dimensional view of a multiple layers of a material that can be used to encompass the sensor capacitor and the reference capacitor in a boxed device, according to one embodiment. Particularly,FIG. 11illustrates a bottom cup1114formed with multiple blocks of material according to one embodiment. A single thin solid metal-block may form a bottom layer1100as illustrated inFIG. 11. In addition, other layers of the bottom cup1114may be formed from layers (e.g., the layers1102A-1102N) each laser cut (e.g., laser etched) and/or patterned (e.g., to form the bottom cup1114at a cost lower than milling techniques in a single block as may be required in the bottom cup1014ofFIG. 10). For example, the layers1102A-1102N may be a standard metal size and/or shape, thereby reducing the cost of fabricating the bottom cup1114.

In one embodiment, the bottom cup1114inFIG. 11replaces the bottom layer of a boxed device, and encompasses the various structures (e.g., capacitive surfaces/plates, spacers, etc.) between a bottom layer and a top plate. Like in the embodiment ofFIG. 10, the bottom cup1114ofFIG. 11may be able to withstand larger amounts of force (e.g., the force105ofFIG. 1) by channeling the force downward through the walls of the bottom cup1114. Furthermore, the bottom cup1114may be less expensive to manufacture than the bottom cup1014as described inFIG. 10because standard machining techniques may be used to manufacture the bottom cup1114.

FIG. 12is a process view to automatically generate a measurement of a force based on an algorithm that considers a change in a capacitance between a fixed surface and a movable surface, according to one embodiment. At operation1202, at least one spring assembly (e.g., the arrangements of conical washers as illustrated inFIGS. 1-4) is positioned between a fixed surface (e.g., the fixed surface170ofFIG. 1) and a movable surface (e.g., the movable surface110ofFIG. 1). At operation1204, a force (e.g., due to the force105ofFIG. 1) is applied perpendicular to the movable surface to cause a change in the height of the at least one spring assembly and to cause a change in a gap between the fixed surface and the movable surface.

At operation1206, at least one spring assembly (e.g., the spring assembly as illustrated inFIG. 2) is deflected longitudinally and perpendicularly to a direction of the force such that a perpendicular deflection does not contact the movable surface and the fixed surface (e.g., the perpendicular deflection at the points of contact with the movable surface and the fixed surface may be negligible). At operation1208, a measurement of a force may be automatically generated based on an algorithm that considers a change in a capacitance between the fixed surface and the movable surface. At operation1210, the measurement of the force may be adjusted based on a change in a reference capacitance (e.g., formed by the surface622and the surface628ofFIG. 6), that is affected primarily because of one or more environmental conditions (e.g., to compensate for changes in the measurement due to environmental conditions).

FIG. 13is a process view to apply a force (due to the force700ofFIG. 7) perpendicular to a movable surface (e.g., the movable surface702ofFIG. 7) to cause a change in a height of the at least one spring assembly (e.g., the spring assembly as illustrated inFIG. 2) and to cause a change in a gap between a fixed surface and the movable surface, according to one embodiment. At operation1302, an elastic device (e.g., the device300ofFIG. 3) is positioned between a movable surface and a fixed surface perpendicular to the movable surface. At operation1304, the elastic device is caused to change form (e.g., contract) based on a force applied adjacent to the movable surface. At operation1306, a measurement of a force is automatically generated (e.g., by a software code and/or hardware) based on a change in an overlap area between a fixed surface and the movable surface. At operation1308, a reference capacitor may be formed by substantially parallel plates of the fixed surface and a reference surface (e.g., as formed by the plate810and the plate816ofFIG. 8). At operation1310, a measurement is adjusted based on a change in capacitance of a reference capacitor whose capacitance changes because of one or more environmental conditions (e.g., temperature and/or humidity)

Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.