Force sensor, strain sensor and methods for measuring same

[0001] The present invention relates generally to sensors and methods for sensing, and more particularly to a force sensor, to a strain sensor, to a method for measuring a force, and to a method for measuring a strain.

[0002] Conventional force sensors include those which place a quantum tunneling composite (QTC) in a load path of a force to be under strain from the force. The electrical resistance of the quantum tunneling composite changes with changes in the force. The conventional QTC force sensors determine the force from a measurement of the electrical resistance. The conventional QTC force sensor is suited to measuring a “point force” at a “point location” on the QTC material because the electrical resistance of the QTC material undergoes a change from applying a point force to a point location on the QTC material but additional loads will reduce the overall resistance of the QTC material (i.e., the QTC material acts like a plurality of resistors connected in parallel). QTC force sensors and quantum tunneling composites (i.e., QTC materials) are available from Peratech Ltd whose www website is peratech.co.uk. Known QTC materials include those whose electrical resistance is temperature dependent.

[0003] Conventional strain gages include those which rely on a change in electrical resistance of a resistor placed under strain. Other conventional methods to measure strain using SAW (surface acoustic wave) technology or magnetostrictive materials are known.

[0004] What is needed is an improved force sensor and an improved strain sensor and methods for measuring same.

[0005] An embodiment of a force sensor of the invention includes a coil, a quantum tunneling composite, and an inductance measuring assembly. The coil is adapted to carry an electric current. The quantum tunneling composite is electrically insulated from the coil, located in a magnetic path created by the coil when an alternating current is present in the coil, and positionable in a load path of a force to be under strain from the force. The inductance measuring assembly is operatively connected to the coil to measure an inductance in the coil when the alternating current is present in the coil and when the quantum tunneling composite is disposed in the load path of the force to be under strain from the force. The force sensor determines the force using at least the measured inductance in the coil.

[0006] A method of the invention for measuring a force includes several steps. One step includes obtaining a coil assembly including a coil and a quantum tunneling composite, wherein the coil is adapted to carry an electric current, and wherein the quantum tunneling composite is electrically insulated from the coil and is disposed in a magnetic path created by the coil when an alternating current is present in the coil. Another step includes positioning the coil assembly with the quantum tunneling composite in a load path of a force and under strain from the force. An additional step includes measuring an inductance in the coil when the alternating current is present in the coil and when the quantum tunneling composite is disposed in the load path of the force and under strain from the force. A further step includes determining the force using at least the measured inductance in the coil.

[0007] An embodiment of a strain sensor of the invention includes a coil, a quantum tunneling composite, and an inductance measuring assembly. The coil is adapted to carry an electric current. The quantum tunneling composite is electrically insulated from the coil, located in a magnetic path created by the coil when an alternating current is present in the coil, and positionable in a load path of a force to be under strain from the force. The inductance measuring assembly is operatively connected to the coil to measure an inductance in the coil when the alternating current is present in the coil and when the quantum tunneling composite is positioned in the load path of the force to be under strain from the force. The strain sensor determines the strain using at least the measured inductance in the coil.

[0008] A method of the invention for measuring a strain includes several steps. One step includes obtaining a coil assembly including a coil and a quantum tunneling composite, wherein the coil is adapted to carry an electric current, and wherein the quantum tunneling composite is electrically insulated from the coil and is located in a magnetic path created by the coil when an alternating current is present in the coil. Another step includes positioning the coil assembly with the quantum tunneling composite in a load path of a force and under strain from the force. An additional step includes measuring an inductance in the coil when the alternating current is present in the coil and when the quantum tunneling composite is positioned in the load path of the force and under strain from the force. A further step includes determining the strain using at least the measured inductance in the coil.

[0009] Several benefits and advantages are derived from one or more of the methods and expressions of the embodiments of the invention. The measured inductance is an average inductance of the coil which changes equally with the addition of equal point loads allowing an average force to be determined. Applicant has successfully performed a proof of principle experiment demonstrating the workability of an example of the method for measuring a force.

[0016] Referring now to the drawing, FIGS. 1–3 show an embodiment of a force sensor 10 of the present invention. A first expression of the embodiment of FIGS. 1–3 is a force sensor 10 which includes a coil 12, a quantum tunneling composite 14, and an inductance measuring assembly 16. The coil 12 is adapted to carry an electric current. The quantum tunneling composite 14 is electrically insulated from the coil 12, is disposed in a magnetic path created by the coil 12 when an alternating current is present in the coil 12, and is disposable in a load path of a force (indicated by the unnumbered arrows in FIG. 3) to be under strain from the force. The inductance measuring assembly 16 is operatively connected to the coil 12 to measure an inductance in the coil 12 when the alternating current is present in the coil 12 and when the quantum tunneling composite 14 is disposed in the load path of the force to be under strain from the force, wherein the force sensor 10 determines the force using at least the measured inductance in the coil 12.

[0017] It is noted that for the purposes of describing the first expression of the embodiment of FIGS. 1–3, the term “force” includes, without limitation, force per unit area (pressure). It is also noted that the direction of the load path of the force can be any direction with respect to the coil 12 provided that the force places the quantum tunneling composite 14 in strain.

[0018] In one application of the first expression of the embodiment of FIGS. 1–3, the inductance measuring assembly 16 supplies the alternating current to the coil 12. In one deployment of the first expression of the embodiment of FIGS. 1–3, the quantum tunneling composite 14 has a temperature, and the force sensor 10 determines the force using at least the temperature of the quantum tunneling composite 14 and the measured inductance in the coil 12.

[0019] In one construction of the embodiment of FIGS. 1–3, the coil 12 comprises a conductor 18 surrounded by electrical insulation 20. In one variation, the quantum tunneling composite 14 surrounds the electrical insulation 20. In this variation, the turns of the conductor 18 together with the surrounding electrical insulation 20 together with the surrounding quantum tunneling composite 14 are referred to as a coil assembly 22. In one modification, the quantum tunneling composite 14 is molded to the electrical insulation 20 and is said to be electrically insulated from the coil 12 because it is electrically insulated from the conductor 18 of the coil 12. In another construction, not shown, the quantum tunneling composite is disposed inside a non-helical or helical coil with the coil surrounding the quantum tunneling composite and with the quantum tunneling composite attached to or spaced apart from the coil. In a further construction, not shown, the quantum tunneling composite is disposed outside a non-helical or helical coil to surround the coil with the quantum tunneling composite attached to or spaced apart from the coil. Other constructions are left to the artisan.

[0020] In one implementation of the embodiment of FIGS. 1–3, the force sensor 10 also includes a lookup table 24 which converts inductance to force. In one variation, the lookup table 24 is an analog or digital circuit. In another variation, the lookup table 24 is stored in computer memory. In one example, the lookup table 24 is empirically determined for the particular force sensor by noting measured inductances for known applied forces. Other implementations for converting inductance to force are left to the artisan.

[0021] A method of the invention for measuring a force is shown in FIG. 4 and includes steps a) through d). Step a) is labeled as “Obtain Coil Assembly” in block 26 of FIG. 4. Step a) includes obtaining a coil assembly 22 including a coil 12 and a quantum tunneling composite 14, wherein the coil 12 is adapted to carry an electric current, and wherein the quantum tunneling composite 14 is electrically insulated from the coil 12 and is disposed in a magnetic path created by the coil 12 when an alternating current is present in the coil 12. Step b) is labeled “Dispose Coil Assembly In Load Path Of Force” in block 28 of FIG. 4. Step b) includes disposing the coil assembly 22 with the quantum tunneling composite 14 in a load path of a force and under strain from the force. Step c) is labeled “Measure Inductance In Coil” in block 30 of FIG. 4. Step c) includes measuring an inductance in the coil 12 when the alternating current is present in the coil 12 and when the quantum tunneling composite 14 is disposed in the load path of the force and under strain from the force. Step d) is labeled as “Determine Force Using Measured Inductance” in block 32 of FIG. 4. Step d) includes determining the force using at least the measured inductance in the coil 12.

[0022] In one employment of the method for measuring a force, the quantum tunneling composite 14 has a temperature, and step d) determines the force using at least the temperature of the quantum tunneling composite 14 and the measured inductance in the coil 12. In one implementation of the method for measuring a force, the coil 12 is an insulated coil having a conductor 18 surrounded by electrical insulation 20. In one variation, the quantum tunneling composite 14 surrounds and is attached to the electrical insulation 20. Other implementations and variations, including those wherein, in the coil assembly 22, the quantum tunneling composite 14 is not attached to the coil 12, are left to the artisan.

[0023] Referring again to the drawing, FIG. 5 shows an embodiment of a strain sensor 34 of the present invention. A first expression of the embodiment of FIG. 5 is a strain sensor 34 which includes a coil 12, a quantum tunneling composite 14, and an inductance measuring assembly 16. The coil 12 is adapted to carry an electric current. The quantum tunneling composite 14 is electrically insulated from the coil 12, is disposed in a magnetic path created by the coil 12 when an alternating current is present in the coil 12, and is disposable in a load path of a force to be under strain from the force. The inductance measuring assembly 16 is operatively connected to the coil 12 to measure an inductance in the coil 12 when the alternating current is present in the coil 12 and when the quantum tunneling composite 14 is disposed in the load path of the force to be under strain from the force, wherein the strain sensor 34 determines the strain using at least the measured inductance in the coil 12.

[0024] It is noted that for the purposes of describing the first expression of the embodiment of FIG. 5, the term “strain” includes, without limitation, change in dimension. It is also noted that the direction of the load path of the force can be any direction with respect to the coil 12 provided that the force places the quantum tunneling composite 14 in strain.

[0025] In one application of the first expression of the embodiment of FIG. 4, the inductance measuring assembly 16 supplies the alternating current to the coil 12. In one deployment of the first expression of the embodiment of FIG. 4, the quantum tunneling composite 14 has a temperature, and the force sensor 10 determines the force using at least the temperature of the quantum tunneling composite 14 and the measured inductance in the coil 12.

[0026] In one construction of the coil 12 of the embodiment of FIG. 4 (such coil construction being identical to that shown in FIGS. 2 and 3), the coil 12 comprises a conductor 18 surrounded by electrical insulation 20. In one variation, the quantum tunneling composite 14 surrounds the electrical insulation 20. In this variation, the turns of the conductor 18 together with the surrounding electrical insulation 20 together with the surrounding quantum tunneling composite 14 are referred to as a coil assembly 22. In one modification, the quantum tunneling composite 14 is molded to the electrical insulation 20 and is said to be electrically insulated from the coil 12 because of the electrical insulation 20. In another construction, not shown, the quantum tunneling composite is disposed inside a non-helical or helical coil with the coil surrounding the quantum tunneling composite and with the quantum tunneling composite attached to or spaced apart from the coil. In a further construction, not shown, the quantum tunneling composite is disposed outside a non-helical or helical coil to surround the coil with the quantum tunneling composite attached to or spaced apart from the coil. Other constructions are left to the artisan.

[0027] In one implementation of the embodiment of FIG. 4, the strain sensor 34 also includes a lookup table 36 which converts inductance to strain. In one variation, the lookup table 36 is an analog or digital circuit. In another variation, the lookup table 36 is stored in computer memory. In one example, the lookup table 36 is empirically determined for the particular strain sensor by noting measured inductances for known strains. Other implementations for converting inductance to strain are left to the artisan.

[0028] A method of the invention for measuring a strain is shown in FIG. 6 and includes steps a) through d). Step a) is labeled as “Obtain Coil Assembly” in block 38 of FIG. 6. Step a) includes obtaining a coil assembly 22 including a coil 12 and a quantum tunneling composite 14, wherein the coil 12 is adapted to carry an electric current, and wherein the quantum tunneling composite 14 is electrically insulated from the coil 12 and is disposed in a magnetic path created by the coil 12 when an alternating current is present in the coil 12. Step b) is labeled “Dispose Coil Assembly In Load Path Of Force” in block 40 of FIG. 6. Step b) includes disposing the coil assembly 22 with the quantum tunneling composite 14 in a load path of a force and under strain from the force. Step c) is labeled “Measure Inductance In Coil” in block 42 of FIG. 6. Step c) includes measuring an inductance in the coil 12 when the alternating current is present in the coil 12 and when the quantum tunneling composite 14 is disposed in the load path of the force and under strain from the force. Step d) is labeled as “Determine Strain Using Measured Inductance” in block 44 of FIG. 6. Step d) includes determining the strain using at least the measured inductance in the coil 12.

[0029] In one employment of the method for measuring a strain, the quantum tunneling composite 14 has a temperature, and step d) determines the strain using at least the temperature of the quantum tunneling composite 14 and the measured inductance in the coil 12. In one implementation of the method for measuring a strain, the coil 12 is an insulated coil having a conductor 18 surrounded by electrical insulation 20. In one variation, the quantum tunneling composite 14 surrounds and is attached to the electrical insulation 20. Other implementations and variations, including those wherein, in the coil assembly 22, the quantum tunneling composite 14 is not attached to the coil 12, are left to the artisan.

[0030] Several benefits and advantages are derived from one or more of the methods and expressions of the embodiments of the invention. The measured inductance is an average inductance of the coil which changes equally with the addition of equal point loads allowing an average force to be determined. Applicant has successfully performed a proof of principle experiment demonstrating the workability of an example of the method for measuring a force.

[0031] The foregoing description of several expressions of embodiments and methods of the invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise form and steps disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.