Patent Description:
Many aircraft components require heating to prevent and minimize ice formation. Specifically, prior art propeller ice protection heaters are wire wound or etched metal foil. Wire wound heaters are time intensive to build. Etched metal foil heaters are made through a wasteful and environmentally unfriendly process that is difficult to control and produces large amounts of scrap. Alternative ice protection heaters have been made with conventional printed circuits, which require a rigid, high energy substrate not suitable for complex geometries or high fatigue environments associated with propeller ice protection.

<CIT> discloses a propeller assembly comprising a heater, the heater comprising: a flexible substrate and a heating element thereon, the heating element comprising a layer of conductive ink containing loaded particles selected from the group consisting of carbon, nano-carbon, and nano-silver particles, wherein the heating element has a thickness of <NUM>, wherein the heating element adheres to, and matches the geometry of a curved component, and wherein the heater is sandwiched between a structural layer and an erosion shield of the propeller assembly such that the heater is embedded within the propeller assembly.

A propeller assembly as defined in claim <NUM> is provided.

A method as defined in claim <NUM> is provided.

Flexible additive manufactured ice protection heaters suitable for propeller and other aircraft component applications can be made by additively manufacturing conductive ink on a flexible substrate. When additively manufactured on a flexible substrate such as a neoprene, TPU, urethane, or fabric, these conductive inks can be integrated into elastomeric propeller ice protection components that will conform and flex to the propeller blade. Alternatively, a heating element made of conductive ink can be directly additively manufactured onto the surface of a propeller through methods such as aerosol jet or ink-jet printing processes.

<FIG> are schematic diagrams of additively manufactured heater <NUM>, and will be discussed together. <FIG> is a top-down view of heater <NUM>, while <FIG> is a side view of heater <NUM> along line A-A. Heater <NUM> includes conductive ink <NUM> on substrate <NUM> covered by encapsulating material <NUM>. Conductive ink <NUM> is electrically connected by leads <NUM> to controller <NUM>.

Heater <NUM> is a three-dimensionally additively manufactured device made of conductive ink <NUM> with a resistivity range of <NUM> to <NUM> circular MIL ohm per foot, depending on the size and specific application of heater <NUM>. Conductive ink <NUM> can have a thickness between approximately <NUM> (<NUM> inches) and <NUM> (<NUM> inches).

Conductive ink <NUM> makes up the additively manufactured, heating portion of heater <NUM>. Conductive ink <NUM> can be a carbon loaded, nano-carbon loaded, or nano-silver loaded ink and can be up to <NUM>% loaded with carbon (or silver) particles. In other embodiments, conductive ink <NUM> can be up to <NUM>% loaded, or at least up to <NUM>% loaded. Conductive ink <NUM> can be, for example, commercially available inks such as Loctite® CT <NUM>, Loctite® Ablestik® 8008MD, Loctite® EDAG 6017SS, or Loctite® EDAG 725A from Loctite, Bonderite® S-FN <NUM> available from Henkel, DuPont® PE671, DuPont® PE873, or DuPont® PE410 from DuPont USA. Alternatively, conductive ink <NUM> can be a positive temperature coefficient (PTC) ink. PTC heaters are self-regulating heaters that run open-loop without any external diagnostic controls. Positive temperature coefficient heaters come to full power and heat up quickly to optimum temperature, but as heat increases, power consumption drops. This dynamic type of heater is effective and time and energy efficient. Thus, heater <NUM> made with PTC conductive ink <NUM> does not require an outside temperature control. Examples of PTC inks include DuPont® <NUM> available from DuPont or Henkel® ECl <NUM> available from Henkel.

The conductive ink <NUM> of heater <NUM> is formulated to allow highly detailed precision printing, and maintain a high resistance without bleeding between adjacent additively manufactured lines. Conductive ink <NUM> is additively manufactured onto substrate <NUM> through a printing process such as screen printing, ink-jet, aerosol-jet printing, or other processes known to provide similar printing capabilities.

Substrate <NUM> can be, for example, a flexible substrate on which conductive ink <NUM> is additively manufactured. Appropriate materials include neoprene, nylon fabric, glass fabric, pre-impregnated fabric (containing a resin), urethane, or other similar materials. Alternatively, conductive ink <NUM> can be additively manufactured directly onto the surface of the component which heater <NUM> will heat.

Conductive ink <NUM> is sealed to substrate <NUM> (or the surface of the component) by encapsulating material <NUM>, which protects conductive ink <NUM> from external contaminants and dielectric failure. Encapsulating materials can include neoprene, nylon fabric, glass fabric, pre-impregnated fabrics, urethane, or other materials that will electrically isolate conductive ink <NUM> from the external environment.

In either case, leads <NUM> create an electrical connection between conductive ink <NUM> and controller <NUM>. Leads <NUM> can be conventional wires, or can be additively manufactured like conductive ink <NUM>.

Controller <NUM> is in communication with heater <NUM> via leads <NUM>. Controller <NUM> powers heater <NUM> ON and OFF based on preset ON and OFF times, or based on temperature feedback from a temperature sensor (not shown).

Controller <NUM> can include one or more processors and controller-readable memory encoded with instructions that, when executed by the one or more processors, cause controller <NUM> to operate in accordance with techniques described herein. Examples of the one or more processors include any one or more of a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry. Controller-readable memory of controller <NUM> can be configured to store information within controller <NUM> during operation. The controller-readable memory can be described, in some examples, as controller-readable storage media. In some examples, a controller-readable storage medium can include a non-transitory medium. The term "non-transitory" can indicate that the storage medium is not embodied in a substrate wave or a propagated signal. In certain examples, a non-transitory storage medium can store data that can, over time, change (e.g., in RAM or cache). Controller-readable memory of controller <NUM> can include volatile and non-volatile memories. Examples of volatile memories can include random access memories (RAM), dynamic random access memories (DRAM), static random access memories (SRAM), and other forms of volatile memories. Examples of non-volatile memories can include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. Controller <NUM> can be a stand-alone device dedicated to the operation of the catalytic oxidation unit, or it can be integrated with another controller.

In operation, heater <NUM> converts electrical input to thermal output on the surface of substrate <NUM> to heat the component on which heater <NUM> rests. Additively manufacture heater <NUM> can also be applied to geometrically complex surfaces. Because present ink technologies are often limited by their ability to carry electrical current, the subject invention is best suited for applications that require lower power densities <<NUM> Watts per square centimeter (<<NUM> watts per square inch), such as propellers.

Conductive ink <NUM> can be manufactured, for example, on a flexible substrate such as substrate <NUM>. Flexible substrate <NUM> must be able to conform to the curvature of the component surface to which heater <NUM> will be applied. The materials for substrate <NUM> are discussed above. In some instances, the substrate must be cleaned or cured before printing using conventional curing methods.

Substrate <NUM> must be compatible with both the component and conductive ink <NUM> used to make the heating element and can be a low energy substrate material. For instance, flexible substrate <NUM> must be able to withstand heating occurring with the component, and maintain adhesion to the component. This is highly dependent on the specific component and conductive ink <NUM> chosen. For example, if the component is a propeller blade, flexible substrate <NUM> must be able to withstand light, temperature, and weather external to the aircraft. Next, conductive ink <NUM> is additively manufactured onto substrate <NUM> in layers to form heater <NUM>. Examples of commercially available conductive inks are discussed above. Typically, ink-jet, aerosol-jet, or screen printing can be used depending on the type of ink chosen,
desired layer thickness, and dimensions of heater <NUM>. For two dimensional printing on a substrate using screen printing, the screen specifications such as mesh count, size, and material are selected based on conductive ink <NUM> being used, the desired thicknesses of conductive ink <NUM> required to be additive manufactured, and the substrate to be additive manufactured on.

For ink-jet and aerosol-jet methods, the print head should be moveable at least on (x, y, z) axes and programmable with the geometric pattern specific to the component on which conductive ink <NUM> will be applied. The specific print head and additively manufacturing method will be dependent on the exact ink formulations and requirements set forth by the manufacturer of the ink. Ink-jet and aerosol-jet printers and printing heads can be utilized for two dimensional applications, such as printing on a substrate, but ideally can be adapted to enable three dimensional printing capabilities by attaching the printing heads onto a numerically controlled robotic arm. For example, three dimensional ink-jet and aerosol-jet printing equipment developed by Ultimaker (three dimensional ink-jet equipment) or Optomec (three dimensional aerosol-jet equipment) can be used. For ink-jet or aerosol-jet methods, the printing head temperatures, flow rates, nozzle sizes are also selected based on the conductive ink being additive manufactured, required conductive ink thickness, and substrate to be additive manufactured on.

The printing is accomplished in an additive manner, meaning the print head takes one or more passes before a desired heater element resistance is reached in the desired geometric pattern and desired dimensions, which matches the curvature of the component. Alternatively, substrate <NUM> can be a rigid substrate already shaped so that it conforms to the geometric surface of the component to which it will be applied. In this case, the additive manufacturing of conductive ink <NUM> must follow a three-dimensional print pattern.

Conductive ink <NUM> of the additively manufactured heater element should have a thickness of approximately between <NUM>-<NUM> (<NUM>" - <NUM>"). Multiple passes are done by the print head when applying conductive ink <NUM>. Each layer deposited through individual passes of the print head should have a thickness of approximately <NUM>-<NUM> microns. Multiple passes allows for slow buildup of conductive ink <NUM> to the correct resistance and geometric pattern. Additionally, multiple passes allows for tailoring of conductive ink <NUM> on certain portions of the component surface. For instance, conductive ink <NUM> with a lower resistance (e.g., with a higher number of layers) and a greater thickness may be additively manufactured on a first portion of the component compared to a second portion of the component.

After additively manufacturing the heating element, conductive ink <NUM> is cured, and leads <NUM> are connected to conductive ink <NUM>. The curing process of additively manufactured conductive ink <NUM> depends on the type of conductive ink <NUM> used. In some instances, conductive ink <NUM> will air dry. In other instances, heat, infrared exposure, UV exposure, or other methods can be used to cure conductive ink <NUM>.

After conductive ink <NUM> is additively manufactured onto substrate <NUM>, it may be encapsulated with a dielectric material, such as acrylic, neoprene, polyurethane, silicone, or an epoxy-fiberglass matrix, to prevent erosion and electrical shorting. For example, encapsulating materials with high dielectric strength may only be required to be <NUM> (<NUM>") thick while materials with lower dielectric strength, such as polyurethane or neoprene rubber, may be as thick as <NUM>-<NUM> (<NUM>-<NUM>"). Encapsulating material <NUM> can then be cured through conventional methods.

Finally, heater <NUM> may be applied to the component surface with an adhesive such as a cement adhesive (for application to a propeller blade or other surface), depending on the component and environment requirements. The flexible substrate <NUM> allows for conforming of heater <NUM> to curvature of the component surface, to which it is applied, without creating unnecessary internal stresses.

Alternatively, conductive ink <NUM> is additively manufactured directly onto the component surface. If conductive ink <NUM> is additive manufactured directly onto the component surface, the printing method used must allow for a print head that can move in three dimensions and navigate the geometry of the component surface while printing. Like the first method, the print head will make multiple passes until the resistance and thickness of conductive ink <NUM> is correct. Methods such as screen printing, ink-jet or aerosol-jet printing can be used, the method would be selected based on the complexity of the shape on which conductive ink <NUM> is being additive manufactured. In some instances, the component surface must be primed or prepared prior to printing of conductive ink <NUM>. The printing process is similar to that described in reference to the first embodiment, but the print head in this embodiment follows a predetermined three-dimensional program to print on the surface of the component. Once additive manufactured, conductive ink <NUM> must be electrically connected, encapsulated, and cured as discussed above.

In some instances, where the assembly surface is electrically conductive (metallic), this necessitates the use of an intermediary dielectric layer between the assembly and additively manufactured conductive ink <NUM>, such as a non-conductive ink like DuPont BQ10 or ME777 available from DuPont USA, or an integrally bonded layer such as an epoxy-fiberglass. The typical thickness of a dielectric layer depends on the dielectric strength of the material and as a result may vary between <NUM> <NUM> (<NUM>" and <NUM>") thick. The dielectric layer is not necessary for certain types of composite surfaces. This dielectric layer is thin, and acts as an insulator and adhesive between the component surface and the additively manufactured conductive ink <NUM>. The dialectic layer, like the flexible substrate in the first embodiment, must be able to withstand temperatures, light, and other environmental factors so that heater <NUM> maintains its adhesion to the component.

In any method of heater <NUM>, heater <NUM> adheres to and matches the geometry of the surface of the component to which it is applied. This allows for greater fatigue resistance over the lifespan of the component and heater <NUM>. Moreover, multiple applications of conductive ink <NUM> allows for varying thickness and resistance of the heating element as needed on the component. Various embodiments of heater <NUM> integrated within components are discussed with reference to <FIG>.

<FIG> is a schematic diagram of heater <NUM> integrated within propeller assembly <NUM>. Propeller assembly <NUM> has, from inside to outside, core <NUM>, structural plies <NUM>, heater <NUM>, erosion shield <NUM>, leads <NUM> and controller <NUM>.

Component assembly <NUM> is a propeller for aircraft with a curved surface. Core <NUM> and structural plies <NUM> make up the internal structure of component <NUM>, providing structural support. Core <NUM> can be, for example, metal, wood, foam, fiberglass, or other material suitable to support propeller assembly <NUM>. Erosion shield <NUM> protects all of assembly <NUM>, including heater <NUM>, from the external environment.

Heater <NUM> internally heats component <NUM>, and can be any embodiment aforementioned above. In <FIG>, heater <NUM> is pictured with substrate <NUM>, conductive ink <NUM>, and encapsulating layer <NUM> sandwiched between structural layers <NUM> and erosion shield <NUM> of assembly <NUM>. The layers of heater <NUM> are compiled and additively manufactured during the assembly of propeller assembly <NUM>. In this way, the parts of heater <NUM> (substrate <NUM>, conductive ink <NUM>, encapsulating layer <NUM>) are layers of propeller assembly <NUM>. Embedded in the middle of assembly <NUM>, heater <NUM> is electrically connected to controller <NUM> via leads <NUM>, and protected from external and environmental factors.

Conductive ink <NUM> of heater <NUM> can be printed with varying resistance. For example, in a first portion of heater <NUM>, conductive ink <NUM> can have a higher power density. In a second portion of heater <NUM>, conductive ink <NUM> can have a lower power density. This can be tailored depending on power density needs across the component requiring heating. Additionally, additive manufactured ice protection heating elements can be printed in complex geometric patterns, such as redundant paths or patterns that increase resistance to foreign object damage.

<FIG> are schematic diagrams of an additively manufactured heater <NUM> on propeller <NUM> in a second embodiment, and will be discussed together. <FIG> is a perspective view of propeller assembly <NUM>, while <FIG> is a cross sectional view along line B-B of <FIG>. Propeller assembly <NUM> contains core <NUM>, structural layers <NUM>, and erosion shield <NUM>, in addition to heater <NUM>, leads <NUM>, and controller <NUM>. These are many of the same components as those in <FIG>. Varying components will be discussed in depth.

In assembly <NUM>, heater <NUM> is additively manufactured conductive ink <NUM> on the curved surface of and conforming to the geometry of assembly <NUM>. Alternatively, conductive ink <NUM> can reside on a flexible substrate which is attached to the curvature of assembly <NUM>. Leads <NUM> connect heater <NUM> to an electrical source and allow for communication with a controller as heater <NUM> heats the surface of assembly <NUM>. As discussed with reference to <FIG>, conductive ink <NUM> can be printed with varying resistance.

High flexure, composite propeller blades are common. Evidence supports additive manufactured ice protection heating elements on flexible substrates may offer greater fatigue resistance on these types of propeller blades. Finally, additive manufactured ice protection heating elements are lighter weight than traditional wound wire or etched metallic heating elements.

Claim 1:
A propeller assembly (<NUM>) comprising a heater (<NUM>),
the heater (<NUM>) comprising:
a flexible substrate (<NUM>); and
a heating element thereon, the heating element comprising a plurality of layers of conductive ink (<NUM>) containing loaded particles selected from the group consisting of carbon, nano-carbon, and nano-silver particles , each layer of the plurality of layers being deposited through individual passes of a print head;
wherein the heating element includes a first portion with a first power density and a second portion with a second power density that is different than the first power density;
wherein the heating element has a thickness between <NUM> and <NUM> ;
wherein the heating element adheres to, and matches the geometry of, a curved component;
wherein the layers of conductive ink are arranged in such a way as to provide redundant paths; and
wherein the heater (<NUM>) is sandwiched between a structural layer (<NUM>) and an erosion shield (<NUM>) of the propeller assembly (<NUM>) such that the heater (<NUM>) is embedded within the propeller assembly (<NUM>).