A heating blanket is disclosed. The heating blanket may include a thermoplastic matrix configured to become conformable at a predetermined temperature, a conductor embedded in the thermoplastic matrix and configured to receive electrical current and generate a magnetic field in response to the electrical current, and a plurality of susceptors embedded in the thermoplastic matrix and composed of a magnetic material having a Curie point.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to heating blankets and, more particularly, to a heating blanket and method for heating a structure to a substantially uniform temperature across the structure.

BACKGROUND OF THE DISCLOSURE

Heating blankets can be used for many different purposes. In industrial applications, for example, heating blankets may be used in manufacturing and repair of composite structures by providing a localized application of heat. However, conventional heating blankets do not provide uniform temperatures across an area that is being heated, especially if that area has contoured surfaces. As a result, differential heating across the area causes certain spots to be over-heated while other spots are under-heated.

SUMMARY OF THE DISCLOSURE

In accordance with one embodiment, a method for heating a contoured surface is disclosed. The method may include placing on the contoured surface a heating blanket including a conductor configured to generate a magnetic field in response to an electrical current, a plurality of susceptors configured to generate heat in response to the magnetic field and composed of a magnetic material having a Curie point, and a matrix surrounding the conductor and the plurality of susceptors and composed of a material that becomes conformable at a first predetermined temperature. The method may also include providing electrical current to the heating blanket to increase a temperature of the matrix to at least the first predetermined temperature, and allowing the heating blanket to conform to the contoured surface.

In a refinement, the method may further include increasing the electrical current to the heating blanket to increase the temperature of the matrix to a second predetermined temperature.

In another refinement, the method may further include providing an uncured composite patch on the contoured surface before placing the heating blanket on the contoured surface.

In another refinement, the method may further include providing a vacuum bag assembly over the uncured composite patch and the heating blanket, and applying a vacuum to the vacuum bag assembly before providing electrical current to the heating blanket.

In another refinement, the method may further include supplying electrical current to the heating blanket to maintain the second predetermined temperature for a predetermined time period until the uncured composite patch is cured.

In accordance with another embodiment, a method for repairing a contoured surface of a structure is disclosed. The method may include inserting an uncured composite patch on the contoured surface of the structure, and placing on the uncured composite patch a heating blanket including a thermoplastic matrix, a conductor embedded in the thermoplastic matrix and configured to generate a magnetic field in response to an electrical current, and a plurality of susceptors embedded in the thermoplastic matrix, configured to generate heat in response to the magnetic field, and composed of a magnetic material having a Curie point.

The method may also include installing a vacuum bag assembly over the uncured composite patch and the heating blanket, and applying a vacuum to the vacuum bag assembly. The method may also include providing electrical current to the conductor to increase a temperature of the heating blanket to a first predetermined temperature, and continuing supply of electrical current to the conductor to maintain the first predetermined temperature such that the thermoplastic matrix becomes conformable and conforms to the contoured surface of the structure.

In a refinement, the method may further include increasing the electrical current to the conductor to increase the temperature of the heating blanket to a second predetermined temperature, and continuing supply of the increased electrical current to the conductor to maintain the second predetermined temperature for a predetermined time period to complete curing of the uncured composite patch.

In another refinement, the method may further include ceasing supply of electrical current to the conductor, allowing the temperature of the heating blanket to reach a room temperature, removing the vacuum bag assembly, and removing the heating blanket from the contoured surface of the structure.

In accordance with another embodiment, a heating blanket is disclosed. The heating blanket may include a thermoplastic matrix configured to become conformable at a predetermined temperature, a conductor embedded in the thermoplastic matrix and configured to receive electrical current and generate a magnetic field in response to the electrical current, and a plurality of susceptors embedded in the thermoplastic matrix and composed of a magnetic material having a Curie point.

In a refinement, the thermoplastic matrix may be preformed to a shape of a contoured composite structure.

In another refinement, the Curie point of the plurality of susceptors may be greater than the predetermined temperature of the thermoplastic matrix.

In another refinement, the thermoplastic matrix may be composed of polyethylene.

In another refinement, the plurality of susceptors may comprise at least a first alloy susceptor wire having a first Curie point and a second alloy susceptor wire having a second Curie point different than the first Curie point.

In another refinement, the heating blanket may further comprise reinforcing fibers configured to reduce deformation of the conductor in the thermoplastic matrix.

In another refinement, the reinforcing fibers may surround the conductor and the plurality of susceptors.

In another refinement, the conductor may comprise a plurality of Litz wires arranged in parallel, and the heating blanket may further include a plurality of threads tying the plurality of Litz wires together.

In another refinement, the conductor may comprise a plurality of Litz wires arranged in a knitted configuration.

In another refinement, the conductor may comprise a plurality of Litz wires arranged in a sine wave configuration.

In another refinement, the thermoplastic matrix may include: a first thermoplastic material embedding the conductor and the plurality of susceptors therein, and a second thermoplastic material surrounding the first thermoplastic material, the second thermoplastic material having a minimum viscosity temperature that is lower than a minimum viscosity temperature of the first thermoplastic material.

In another refinement, the heating blanket may be preformed to a shape of a contoured composite structure.

These and other aspects and features will become more readily apparent upon reading the following detailed description when taken in conjunction with the accompanying drawings. In addition, although various features are disclosed in relation to specific exemplary embodiments, it is understood that the various features may be combined with each other, or used alone, with any of the various exemplary embodiments without departing from the scope of the disclosure.

While the present disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof will be shown and described below in detail. The disclosure is not limited to the specific embodiments disclosed, but instead includes all modifications, alternative constructions, and equivalents thereof.

DETAILED DESCRIPTION

Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Generally, corresponding reference numbers will be used throughout the drawings to refer to the same or corresponding parts.

FIG. 1illustrates a perspective cutaway view of a heating blanket20, in accordance with an embodiment of the present disclosure. The heating blanket20may comprise a matrix24with a conductor26and a plurality of susceptors28embedded therein. Although not required, the heating blanket20may also include a housing22, as shown inFIG. 2, that contains the matrix24. The housing22may be made of a same material as the matrix24.

Referring back toFIG. 1, the matrix24is composed of a thermoplastic material or other suitable material that becomes conformable, pliable, or moldable above a minimum viscosity temperature and solidifies upon cooling. In addition, the thermoplastic material of the matrix24is thermally conductive. For example, the thermoplastic material may be polyethylene. Polyethylene has a minimum viscosity temperature between an approximate range of 210° F. to 240° F. However, other thermoplastic materials may be used. By using thermoplastic material for the matrix24, the heating blanket20can stretch and conform to contoured surfaces once the minimum viscosity temperature is achieved. In so doing, the heating blanket20can provide uniform heat to an area to which the heating blanket20is applied.

Embedded within the matrix24, the conductor26may be configured to receive an electrical current and generate a magnetic field in response to the electrical current. In one example, the conductor26may comprise a Litz wire, although other suitable types of conductors can be used as well. Referring now toFIG. 3, with continued reference toFIG. 1andFIG. 2, the conductor26is operatively connected to a portable or fixed power supply36, such as via wiring38. The power supply36may provide alternating current electrical power to the conductor26and may be connected to a conventional outlet.

In addition, the power supply36may operate at higher frequencies. For example, the minimum practical frequency may be approximately ten kilohertz, and the maximum practical frequency may be approximately four hundred kilohertz. However, other frequencies may be used. Furthermore, the power supply36may be connected to a controller40and a voltage sensor42or other sensing device configured to indicate a voltage level provided by the power supply36. Based on the indicated voltage level from the voltage sensor42, the controller40may adjust the alternating current of the power supply36over a predetermined range in order to facilitate application of the heating blanket20to various heating requirements.

Also embedded within the matrix24, the plurality of susceptors28are configured to generate heat in response to the magnetic field generated by the conductor26. More specifically, the plurality of susceptors28absorb electromagnetic energy from the conductor26and convert it to heat. Furthermore, the plurality of susceptors28are composed of a magnetic material having a Curie point. The Curie point is a temperature at which the plurality of susceptors28becomes non-magnetic.

Upon approaching the Curie point, the heat generated by the plurality of susceptors28decreases. For example, if the Curie point of the magnetic material for the plurality of susceptors is 125° F., the plurality of susceptors28may generate two Watts per square inch at 100° F., may decrease heat generation to one Watt per square inch at 110° F., and may further decrease heat generation to 0.5 Watts per square inch at 120° F. As such, portions of the heating blanket20that are cooler due to larger heat sinks generate more heat and portions of the heating blanket20that are warmer due to smaller heat sinks generate less heat, thereby resulting in all portions of the heating blanket20arriving at approximately a same equilibrium temperature and reliably providing uniform temperature over the entire heating blanket20.

Thus, the heating blanket20may provide uniform application of heat to the area to which the heating blanket20is applied, compensating for heat sinks that draw heat away from portions of the area that is being heated. The plurality of susceptors28will continue to heat portions of the area that have not reached the Curie point, while at the same time, ceasing to provide heat to portions of the area that have reached the Curie point. In so doing, the temperature-dependent magnetic properties, such as the Curie point of the magnetic material used in the plurality of susceptors28, may prevent over-heating or under-heating of areas to which the heating blanket20is applied.

The magnetic material of the plurality of susceptors28may be provided in a variety of compositions, such as a metal, an alloy, a metal oxide, a ferrite, and any other suitable material having a Curie point that approximates any desired temperature. Although other predetermined arrangements may be used, the magnetic material of the plurality of susceptors28may be chosen such that the Curie point is above the desired temperature of the heating application in order to generate sufficient heat at the desired temperature to overcome average heat loss. For instance, the plurality of susceptors28may comprise a plurality of alloy susceptor wires. However, other configurations for the plurality of susceptors28may be used.

In one example, the plurality of susceptors28may be composed of Alloy 32, which has 32% Ni and 68% Fe and provides uniform temperatures compensating for heat sinks in the range of about 240° F. to 300° F. In other examples, the magnetic material of the plurality of susceptors28may comprise Alloy 30, which has 30% Ni and 70% Fe for a desired temperature of about 100° F., or Alloy 34, which has 34% Ni and 66% Fe for a desired temperature of about 400° F. However, other compositions may be used for the magnetic material of the plurality of susceptors28. In addition, the heat generation of the plurality of susceptors28may also depend on a diameter of each wire.

Moreover, the plurality of susceptors28may include two or more different magnetic materials. For example, the plurality of susceptors28may include a plurality of first susceptors44composed of a first magnetic material and a plurality of second susceptors46composed of a second magnetic material. The first magnetic material of the plurality of first susceptors44may have a different Curie point than a Curie point of the second magnetic material of the plurality of second susceptors46. By incorporating different magnetic materials having different Curie points into the plurality of susceptors28, increased temperature regulation over a wider range of temperatures may be achieved.

Furthermore, the thermoplastic material of the matrix24may be matched with a compatible magnetic material for the plurality of susceptors28. More specifically, the Curie point of the magnetic material of the plurality of susceptors28may be greater than or at least equal to the minimum viscosity temperature at which the thermoplastic material of the matrix24becomes conformable, pliable, or moldable. In so doing, the plurality of susceptors28heats the matrix24to the minimum viscosity temperature such that the matrix can conform to contoured surfaces, thereby applying uniform temperature to the structure being heated.

In addition, the magnetic material of the plurality of susceptors28may be matched to the application or use of the heating blanket20. More specifically, the Curie point of the plurality of susceptors28may be matched to the desired temperature of the induction heating operation being performed. For example, the plurality of susceptors28may be formed of magnetic materials having Curie points in the range of the curing temperature of the adhesive, epoxy, or composite material, which the heating blanket20is being used to heat.

The conductor26and the plurality of susceptors28may be provided in a variety of configurations within the matrix24. For example, as shown inFIG. 3, the conductor26may be arranged as a flattened helical wire, such as a Litz wire that is wound in a flattened helical or solenoid structure, so as to define a plurality of alternating conductor portions. In the example, the plurality of susceptors28may be arranged as a linear wire array positioned within the alternating conductor portions of the flattened helical wire.

For instance, susceptor wires of the linear wire array may be arranged perpendicular to conductor portions of the flattened helical wire such that a longitudinal axis of the susceptor wires resides substantially perpendicular to an electrical current flowing through the flattened helical wire. In the presence of an electrical current provided by the power supply36, the plurality of susceptors28are positioned between alternating conductor portions of the conductor26for inductive heating of the plurality of susceptors28. The inductively heated plurality of susceptors28thermally conducts heat to the matrix24, which thermally conducts heat to a structure to which the heating blanket20is mounted.

In another example, the plurality of susceptors28may be formed as a solid or unitary component in a cylindrical arrangement. For instance, as shown inFIG. 4, a susceptor48can be configured as a spiral or spring around the conductor26in order to enhance the flexibility of the heating blanket20. However, other arrangements of the conductor26and the plurality of susceptors28may be used.

In addition, the conductor26may comprise a plurality of conductors which are electrically connected in parallel in order to minimize a magnitude of the voltage required for large sized heating blankets. For instance, as shown inFIG. 5, the conductor26may comprise a plurality of Litz wires50arranged parallel to each other. In the example, the plurality of susceptors28comprise a woven fabric of susceptor wires surrounding and substantially aligned circumferentially around each of the Litz wires50. The woven fabric of susceptor wires may include other non-electrically conducting threads to form a reinforcing fabric sleeve around each of the Litz wires50.

Turning now toFIG. 6, with continued reference toFIGS. 1-5, the heating blanket20is reusable and may contain structural elements, such as reinforcing fibers52, to support the reusability of the matrix24. The reinforcing fibers52are used to reduce deformation of the conductor26and the plurality of susceptors28within the matrix24. In addition, the reinforcing fibers52may allow the matrix24to be conformable in one direction and non-conformable in an opposite direction, depending on the placement of the reinforcing fibers52within the matrix24. For example, when the matrix24is heated to the minimum viscosity temperature of the thermoplastic material such that the matrix24stretches and conforms to the part the heating blanket20is applied to, the conductor26and the plurality of susceptors28may move, stretch, or deform within the matrix24. After the matrix24cools and becomes solid again, the conductor26and the plurality of susceptors28may be in a different location within the matrix24than originally positioned before heating of the matrix24to the minimum viscosity temperature of the thermoplastic material.

The reinforcing fibers52may be disposed in the matrix24, such as surrounding the conductor26and the plurality of susceptors28proximate surfaces54,56of the matrix24. In so doing, the reinforcing fibers52help prevent the conductor26and the plurality of susceptors28from breaking through the matrix24. For instance, the reinforcing fibers52may comprise nylon wires, polyester wires, and other types of plastic or textile materials. However, any suitable non-plastic or non-textile materials may be used for the reinforcing fibers52as well. The reinforcing fibers52may be arranged unidirectional, woven or fabric, random or discontinuous fiber mat, or any other suitable arrangement. Furthermore, the housing22may contain reinforcing fibers52in addition to or instead of the matrix24. The reinforcing fibers52may serve as a barrier to reinforce surfaces54,56, while still allowing conformability of the thermoplastic matrix24.

Referring now toFIGS. 7-9, with continued reference toFIGS. 1-6, the heating blanket20may include other structural elements to support reusability, such as textile features58,62,64. More specifically, as shown inFIG. 7, a plurality of threads58composed of nylon, or other suitable materials, are disposed across the Litz wires50and tied to the Litz wires50, such as via knots60. As shown inFIG. 8, the Litz wires50may be interlaced together in a knitted configuration62. The threads58and the knitted configuration62may tie the Litz wires50together and help contain them within the matrix24.

As shown inFIG. 9, the Litz wires50may be formed in a sine wave configuration64, or other suitable pattern. The sine wave configuration64, as well as the threads58and the knitted configuration62, help limit deformation by accommodating stretching of the matrix24. More specifically, such features may provide additional elasticity and spring-back through the conductor26and the plurality of susceptors28embedded within the matrix24. Although inFIGS. 7-9, the Litz wires50are shown and described as incorporating the textile features58,62,64, the plurality of susceptors28may incorporate the textile features58,62,64in addition to or instead of the Litz wires50.

Turning now toFIG. 10, with continued reference toFIGS. 1-9, the matrix24may include various layers66,68,70of thermoplastics having different melting properties. For example, the conductor26and the plurality of susceptors28may be embedded in the internal layer66, while surface layers68,70may surround and encapsulate the internal layer66. In the example, the internal layer66is composed of a first thermoplastic material, and the surface layers68,70are composed of a second thermoplastic material that is different from the first thermoplastic material.

More specifically, the first thermoplastic material and the second thermoplastic material may have different minimum viscosity temperatures at which each material becomes conformable, pliable, or moldable. For instance, the minimum viscosity temperature of the first thermoplastic material in the internal layer66may be greater than the minimum viscosity temperature of the second thermoplastic material in the surface layers68,70. In so doing, the surface layers68,70may become conformable at a lower temperature than the internal layer. At the lower temperature, as the surface layers68,70conform to the contoured surfaces of the part being heated by the heating blanket20, the internal layer66may retain its shape, thereby minimizing deformation of the matrix24while still providing uniform heat to the part.

Referring now toFIGS. 11 and 12, with continued reference toFIGS. 1-10, the heating blanket20may be mounted to a structure72, such as a composite structure, having at least one contoured surface74. The heating blanket20may be used to apply uniform heat to a rework area76on the contoured surface74of the structure72. For example, the heating blanket20may apply heat to cure an adhesive bonding a patch78, such as an uncured composite patch or other type or patch, to the rework area76and/or to heat composite material in the rework area76. However, the heating blanket20may be used to apply uniform heat to non-contoured surfaces of the structure72and to other non-repair applications as well.

Turning now toFIG. 13, with continued reference toFIGS. 1-12, a vacuum bag assembly80may be installed over the heating blanket20to apply pressure to the heating blanket20, such as prior to supplying electrical current to the heating blanket20. The vacuum bag assembly80may include a bagging film82covering the heating blanket20. The bagging film82may be sealed to the contoured surface74of the structure72by means of a sealant84, and a vacuum probe86may extend from the bagging film82to a vacuum generator to apply a vacuum on the bagging film82.

After vacuum pressure is applied via the vacuum bag assembly80to the heating blanket20on the contoured surface74of the structure72, for example, the heating blanket20may still need to stretch and conform to a radius of curvature88of the contoured surface74. The thermoplastic material of the matrix24may provide the necessary elasticity to stretch and conform to the radius of curvature88upon heating of the matrix24to the minimum viscosity temperature by the plurality of susceptors28. For instance, if the radius of curvature88may be 0.1 inches, and the elasticity of the matrix24is about thirty percent, the heating blanket20can sufficiently stretch and conform to the radius of curvature88, as shown inFIG. 14, thereby providing uniform heat across the entire rework area76on the contoured surface74. With vacuum pressure, all portions of the rework area76may be in contact with the heating blanket20and receive the same temperature.

Referring now toFIG. 15, with continued reference toFIGS. 1-14, the heating blanket20may be preformed in an approximate shape of90the structure72. For example, the matrix24may be heated and formed to the approximate shape90of the contoured surface74, then allowed to cool such that at room temperature the heating blanket20retains the preformed shape90. In the example where the radius of curvature88is 0.1 inches, for instance, the heating blanket20may have a preformed radius of curvature of 0.5 inches. However, other preformed shapes and dimensions for the matrix24and the heating blanket20may be used. Moreover, the heating blanket20may be applied to various curvatures and contours than that shown inFIGS. 11-14. The heating blanket20with the preformed shape90or preformed curvature may require less conformability to match the contour of the structure72to which the heating blanket is applied.

In general, the foregoing disclosure provides numerous technical effects and benefits in various applications relating to heating blankets. Particularly, the foregoing disclosure provides a highly formable smart susceptor heating blanket. For example, the disclosed heating blanket can be used in industrial applications during manufacturing and repair of composite structures, and in other applications. The disclosed heating blanket provides uniform, controlled heating of surface areas, such as contoured surface areas.

More specifically, the thermoplastic material of the heating blanket matrix provides elasticity and stretching to conform to contoured surfaces in order to uniformly contact the structure being heated. In addition, the Curie point of the magnetic material in the plurality of susceptors is used to control temperature uniformity in the area to which the heating blanket is applied. With vacuum pressure, all portions of the area being heated may be in contact with the heating blanket and achieve the same temperature, thereby helping to prevent over-heating or under-heating of certain portions of the area being heated. Furthermore, structural elements, such as reinforcing fibers, textile features, and/or layered thermoplastics, may help limit deformation of the matrix and support the reusability of the heating blanket for multiple applications.

Referring now toFIGS. 16 and 17, with continued reference toFIGS. 1-15, a process100for heating a contoured surface74of a structure72, such as for repairing the contoured surface74, is disclosed, in accordance with another embodiment. At block102, an uncured composite patch78is provided or inserted on the contoured surface74of the structure72. At block104, a heating blanket20is placed on the uncured composite patch78on the contoured surface74.

The heating blanket20includes a conductor26configured to generate a magnetic field in response to an electrical current and a plurality of susceptors28configured to generate heat in response to the magnetic field and composed of a magnetic material having a Curie point. The heating blanket20also includes a matrix24surrounding and embedding the conductor26and the plurality of susceptors28. The matrix is composed of a material that becomes conformable at a first predetermined temperature, such as a thermoplastic material. The first predetermined temperature may be a minimum viscosity temperature of the material.

At block106, a vacuum bag assembly80is provided or installed over the uncured composite patch78and the heating blanket20. A vacuum is applied to the vacuum bag assembly80, at block108. Electrical current is provided to the conductor26of the heating blanket20, at block110, to increase a temperature of the matrix24of the heating blanket20to at least the first predetermined temperature. At block112, the heating blanket20is allowed to conform to the contoured surface74. Supply of the electrical current to the conductor26of the heating blanket20may be continued for a first predetermined time period to maintain the first predetermined temperature and to allow the matrix24of the heating blanket20to become conformable, stretch and conform to the contoured surface74of the structure72.

The electrical current to the conductor26of the heating blanket20is increased, at block114, in order to increase the temperature of the matrix24to a second predetermined temperature. The second predetermined temperature may be a desired temperature of the heating operation, such as a curing temperature of the uncured composite patch78. Supply of the increased electrical current to the conductor26of the heating blanket20may be continued to maintain the second predetermined temperature for a second predetermined time period until the uncured composite patch78is cured, at block116.

Furthermore, it is not necessary to maintain supply of the electrical current for the first predetermined time period and/or the second predetermined time period in order to achieve the predetermined temperatures. To achieve a similar effect, the heating blanket20may include two or more different magnetic materials in the plurality of susceptors28for increased temperature regulation over a wider range of temperatures. Moreover, instead of having predetermined time periods, the heating blanket20may be heated from a start temperature, such as room temperature, to a final temperature at a steady rate that allows for the matrix24to conform to the structure72as the heating blanket20steadily increases to the final temperature.

At block118, supply of electrical current to the conductor26of the heating blanket20is ceased, and the temperature of the heating blanket20is allowed to cool or reach a room temperature. The vacuum pressure may be released from the vacuum bag assembly80, and the vacuum bag assembly is removed from the heating blanket20and the contoured surface74of the structure72, at block120. At block122, the heating blanket20is removed from the contoured surface74of the structure72.

Furthermore, embodiments of the disclosure may be described in the context of an aircraft manufacturing and service method200as shown inFIG. 18and an aircraft202as shown inFIG. 19. For example, the heating blanket20may be used during component manufacturing208or during maintenance and service216for repair applications. More specifically, during pre-production, exemplary method200may include specification and design204of the aircraft202and material procurement206. During production, component and subassembly manufacturing208and system integration210of the aircraft202takes place. Thereafter, the aircraft202may go through certification and delivery212in order to be placed in service214. While in service by a customer, the aircraft202is scheduled for routine maintenance and service216(which may also include modification, reconfiguration, refurbishment, and so on).

As shown inFIG. 19, the aircraft202produced by exemplary method200may include an airframe218with a plurality of systems220and an interior222. Examples of high-level systems220include one or more of a propulsion system224, an electrical system226, a hydraulic system228, and an environmental system230. Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry.

Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method200. For example, components or subassemblies corresponding to production process208may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft202is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages208and210, for example, by substantially expediting assembly of or reducing the cost of an aircraft202. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft202is in service, for example and without limitation, to maintenance and service216.

It is to be understood that the flowcharts inFIGS. 16-18are shown and described as an example only to assist in disclosing the features of the disclosed system and techniques, and that more or less steps than that shown may be included in the process corresponding to the various features described above for the disclosed system without departing from the scope of the disclosure.

While the foregoing detailed description has been given and provided with respect to certain specific embodiments, it is to be understood that the scope of the disclosure should not be limited to such embodiments, but that the same are provided simply for enablement and best mode purposes. The breadth and spirit of the present disclosure is broader than the embodiments specifically disclosed and encompassed within the claims appended hereto. Moreover, while some features are described in conjunction with certain specific embodiments, these features are not limited to use with only the embodiment with which they are described, but instead may be used together with or separate from, other features disclosed in conjunction with alternate embodiments.