Patent Description:
In the same way that a building can be constructed by successively adding bricks at specific locations and in a specific order, it is well known in the field of additive manufacturing that an article of manufacture can be fabricated by successively adding segments of fiber-reinforced thermoplastic filament at specific locations and in a specific order. A segment of filament is long, thin, and resembles a wet spaghetti when it is heated above a first temperature and a dry spaghetti when it is cooled below a second temperature.

Adding a segment of filament involves three tasks:.

Each of these will be discussed in turn.

The task of determining where each segment of filament should be placed is performed by an engineer, a computer-aided design system, or both. Although the task can be performed before the first segment of filament has been added, it can also be performed in real-time during manufacturing to compensate for any discrepancy between where a segment of filament was actually added in contrast to where it should have been added. The location where the longitudinal axis of a segment of filament should be added is called the "target path.

Because a segment of filament cannot defy gravity and float in air, the segment of filament must be wholly or partially deposited onto the surface of a supporting structure. Short segments of filament can be cantilevered or suspended, but substantial portions of the segments must be directly undergirded. The supporting structure for a segment of filament can be, but is not limited to:.

Because the target path represents the location where the longitudinal axis of a segment of filament should be added, the target path is near - but not coincident with - the surface of the supporting structure. In most cases, the target path follows the contour of the surface of the adjacent supporting structure.

The task of depositing a segment of filament at the desired location involves laying down a length of the segment of filament so that the longitudinal axis of the segment exactly coincides with the target path.

The task of tamping a segment of filament involves pressing the filament into the underlying supporting structure to ensure:.

Typically, the task of tamping a segment of filament is accomplished by steering a wheel along the length of filament in a similar manner to how laminates and veneers are rolled.

In general, the success of additive manufacturing with segments of filament depends on the ability of the system to add each segment of filament exactly along the target path. Alas, there are circumstances in which this is not readily achievable.

Some embodiments of the present invention are capable of adding a segment of filament to a supporting structure without some of the costs and disadvantages for doing so in the prior art. In particular, some embodiments of the present invention are able to add a segment of filament to a supporting structure with more spatial precision than in the prior art.

In some embodiments of the prior art, the task of depositing a segment of filament is finished before tamping the segment is begun. In other words, a segment of filament is deposited along a target path, and, after all of the filament has been deposited, the segment is then tamped. For a variety of reasons, this is disadvantageous.

In some alternative embodiments of the prior art - and in accordance with the illustrative embodiment - the task of depositing is performed concurrently with the task of tamping. To help understand this, consider four adjacent portions of a segment of filament:.

In this context the inventors of the present invention discovered that when a target path contains a curve (either planar or non-planar), the segment of filament is added outside of the target path instead of along the target path (as shown, for example, in <FIG>, where the location of filament <NUM> does not coincide with target path <NUM>).

To understand the problem, the reader must understand how the second portion is guided into the target path for deposition. In accordance with the prior art and the illustrative embodiment, the second portion is not directly guided into the target path. No machinery or mechanism directly touches the second portion.

Instead, the second portion is guided, indirectly, by virtue of its position between the first and third portions. In other words, as long as it is free to move, the second portion will exist in a straight line between the first and third portions because of the tension between the first and third portions.

Whereas the first portion's location while being tamped is fixed, the third portion's location is being moved laterally in order to guide the second portion into the target path. To accomplish this in a curve, the third portion must be moved outside of the curve on a tangent of the curve. Thereafter, while the second portion is tamped on the target path, the fourth portion's location is being moved laterally in order to guide the third portion into the target path.

In practice, however, the inventors discovered that the wheel is simultaneously:.

This problem could be ameliorated by using a wheel with a small radius but that does not eliminate problem and there are disadvantages to using a small wheel.

Another solution involves changing the way that the wheel is steered along the filament. In the prior art and in accordance with the illustrative embodiment, the wheel is steered along the filament so that the wheel's yaw axis intersects and advances along the target path. The prior art and the illustrative embodiment, however, choose different lines for the wheel's yaw axis. These lines are partially defined with respect to the line around which the wheel is substantially symmetric - the wheel's pitch axis.

In the prior art, a line that intersects the wheel's pitch axis is chosen as the wheel's yaw axis. In contrast, and in accordance with the illustrative embodiment, a line that is offset from the wheel's pitch axis is chosen as the wheel's yaw axis.

The magnitude of the offset depends on several factors, including:.

Furthermore, because the curvature of a target path can change at different locations along the target path, the magnitude of the offset can change at different locations along the target path, and, therefore, the magnitude of the offset - and the location of the wheel's yaw axis relative to its pitch axis - is dynamically adjusted as the wheel advances along the target path.

The illustrative embodiment comprises: depositing a filament on a surface of a supporting structure along a target path; and tamping the filament onto the supporting structure with a wheel by steering the wheel along the filament; wherein the wheel comprises: (i) a pitch axis around which the wheel is substantially symmetric; and (ii) a circumferential surface that comprises: (ii-a) a nip line segment where the circumferential surface exerts maximum radial force on a first length of the filament, and (ii-b) a pinch line segment where the wheel first pinches a second length of the filament between the circumferential surface and the supporting structure so that any movement of the second length of the filament parallel to the pitch axis is substantially constrained; and (iii) a yaw axis that: (iii-a) is perpendicular to the pitch axis, and (iii-b) has a non-zero offset s from the pitch axis, wherein s is a positive real number, and (iii-c) intersects the pinch line segment; and (iv) a roll axis that intersects the pitch axis and the yaw axis and is perpendicular to the pitch axis and the yaw axis; and wherein steering the wheel comprises moving the wheel so that the yaw axis intersects and advances along the target path.

<FIG> depicts an illustration of the salient components of additive manufacturing system <NUM> in accordance with the illustrative embodiment of the present invention. Additive manufacturing system <NUM> comprises: platform <NUM>, robot mount <NUM>, robot arm <NUM>, build plate support <NUM>, build plate <NUM>, supporting structure <NUM>, deposition head <NUM>, tamping tool <NUM>, controller <NUM>, filament reel <NUM>, filament <NUM>, and build volume <NUM>. The purpose of manufacturing system <NUM> is to fabricate an article of manufacture by successively depositing finite lengths of filament on top of each other.

Platform <NUM> is a rigid structure that ensures that the relative spatial relationship of robot mount <NUM>, robot arm <NUM>, deposition head <NUM>, and tamping tool <NUM> are maintained and known with respect to build-plate support <NUM>, build plate <NUM>, and supporting structure <NUM>. It will be clear to those skilled in the art how to make and use platform <NUM>.

Robot mount <NUM> is a rigid and stable support for robot arm <NUM>. It will be clear to those skilled in the art how to make and use robot mount <NUM>.

Robot arm <NUM> comprises a six-axis mechanical arm that is under the control of controller <NUM>. A non-limiting example of robot arm <NUM> is the IRB <NUM> robot offered by ABB. Robot arm <NUM> is capable of depositing a segment of fiber-reinforced thermoplastic filament from any three-dimensional coordinate in build volume <NUM> to any other three-dimensional coordinate in build volume <NUM> with deposition head <NUM> at any approach angle. Robot arm <NUM> can move tamping tool <NUM> in:.

while rotating the approach angle of tamping tool <NUM> around any line, any planar curve, and any non-planar curve within build volume <NUM>. It will be clear to those skilled in the art how to make and use robot arm <NUM>.

Build plate support <NUM> is a rigid and stable support for build plate <NUM> and supporting structure <NUM>. Build plate support <NUM> comprises a stepper motor - under the control of controller <NUM> - that is capable of rotating build plate <NUM> (and, consequently supporting structure <NUM>) around an axis that is normal to the X-Y plane. It will be clear to those skilled in the art how to make and use build plate support <NUM>.

Build plate <NUM> is a rigid support onto which supporting structure <NUM> is rigidly affixed so that it cannot move or rotate independently of build plate <NUM>. It will be clear to those skilled in the art how to make and use build plate <NUM>.

Supporting structure <NUM> comprises a plurality of finite lengths of filament that have been deposited and tamped into the shape depicted in <FIG>.

Deposition head <NUM> comprises hardware necessary to (i) deposit a finite length of filament <NUM> along target path <NUM> (shown in <FIG>) on supporting structure <NUM>, and to (ii) tamp the filament into supporting structure <NUM> using tamping tool <NUM>, which is a subassembly of deposition head <NUM>. Deposition head <NUM> is described in detail in <CIT>. Furthermore, ancillary details about deposition head <NUM> are described in.

Controller <NUM> comprises the hardware and software necessary to direct build volume <NUM>, robot arm <NUM>, deposition head <NUM>, and build plate support <NUM>, in order to fabricate the article of manufacture. It will be clear to those skilled in the art how to make and use controller <NUM>.

Filament reel <NUM> is a circular reel that stores <NUM> meters of filament <NUM> and feeds that filament to deposition head <NUM>. It will be clear to those skilled in the art how to make and use filament reel <NUM>.

Filament <NUM> comprises a tow of reinforcing fibers that is substantially parallel to its longitudinal axis. In accordance with the illustrative embodiments, filament <NUM> comprises a cylindrical towpreg of contiguous <NUM> carbon fiber that is impregnated with thermoplastic resin. The cross-section of filament <NUM> is circular and has a diameter of <NUM>.

In accordance with the illustrative embodiment, filament <NUM> comprises contiguous carbon fiber, but it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which filament <NUM> has a different fiber composition.

It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which filament <NUM> comprises a different number of fibers (e.g., <NUM>, <NUM>, <NUM>, <NUM>, etc.). It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the fibers in filament <NUM> are made of a different material (e.g., fiberglass, aramid, carbon nanotubes, etc.).

In accordance with the illustrative embodiments, the thermoplastic is, in general, a semi-crystalline polymer and, in particular, the polyaryletherketone (PAEK) known as polyetherketone (PEK). In accordance with some alternative embodiments of the present invention, the semi-crystalline material is the polyaryletherketone (PAEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetheretherketoneketone (PEEKK), or polyetherketoneetherketoneketone (PEKEKK). As those who are skilled in the art will appreciate after reading this specification, the disclosed annealing process, as it pertains to a semi-crystalline polymer in general, takes place at a temperature that is above the glass transition temperature Tg.

In accordance with some alternative embodiments of the present invention, the semi-crystalline polymer is not a polyaryletherketone (PAEK) but another semi-crystalline thermoplastic (e.g., polyamide (PA), polybutylene terephthalate (PBT), poly(p-phenylene sulfide) (PPS), etc.) or a mixture of a semi-crystalline polymer and an amorphous polymer.

When the filament comprises a blend of an amorphous polymer with a semi-crystalline polymer, the semi-crystalline polymer can one of the aforementioned materials and the amorphous polymer can be a polyarylsulfone, such as polysulfone (PSU), polyethersulfone (PESU), polyphenylsulfone (PPSU), polyethersulfone (PES), or polyetherimide (PEl). In some additional embodiments, the amorphous polymer can be, for example and without limitation, polyphenylene oxides (PPOs), acrylonitrile butadiene styrene (ABS), methyl methacrylate acrylonitrile butadiene styrene copolymer (ABSi), polystyrene (PS), or polycarbonate (PC). As those who are skilled in the art will appreciate after reading this specification, the disclosed annealing process, as it pertains to a blend of an amorphous polymer with a semi-crystalline polymer, takes place generally at a lower temperature than a semi-crystalline polymer with the same glass transition temperature; in some cases, the annealing process can take place at a temperature slightly below the glass transition temperature.

When the filament comprises a blend of an amorphous polymer with a semi-crystalline polymer, the weight ratio of semi-crystalline material to amorphous material can be in the range of about <NUM>:<NUM> to about <NUM>:<NUM>, inclusive, or about <NUM>:<NUM> to about <NUM>:<NUM>, inclusive. Preferably, the weight ratio of semi-crystalline material to amorphous material in the blend is between <NUM>:<NUM> and <NUM>:<NUM>, inclusive. The ratio selected for any particular application may vary primarily as a function of the materials used and the properties desired for the printed article.

In some alternative embodiment of the present invention, the filament comprises a metal. For example, and without limitation, the filament can be a wire comprising stainless steel, Inconel (nickel/chrome), titanium, aluminum, cobalt chrome, copper, bronze, iron, precious metals (e.g., platinum, gold, silver, etc.).

Build volume <NUM> is the region in three-dimensional space in which robot arm <NUM> is capable of depositing and tamping filament <NUM>. Supporting structure <NUM> exists completely within build volume <NUM>.

<FIG> depict orthographic front, side, and top views of supporting structure <NUM> in accordance with the illustrative embodiment.

In accordance with the illustrative embodiment, supporting structure <NUM> has a rectangular footprint and is <NUM> wide (i.e., in the Δx direction) and <NUM> deep (i.e., in the Δy direction). The bottom surface of supporting structure <NUM> (i.e., the surface adjacent to build plate <NUM>) is planar, adjacent to build plate <NUM>, and parallel to build plate <NUM>. The top surface of supporting structure <NUM> is non-planar, continuous (i.e., comprises no discontinuities), and described by the equation: <MAT> where x is a real number in the range <NUM> ≤ x ≤ <NUM>.

Although supporting structure <NUM> has a rectangular footprint, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the supporting structure has any footprint.

Although supporting structure <NUM> has a footprint of <NUM> x <NUM>, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention of any size.

Although supporting structure <NUM> has a bottom surface that is planar, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the bottom surface has any form (e.g., planar, non-planar, irregular, convex, concave, hemispherical, etc.).

Although supporting structure <NUM> has a bottom surface that is continuous, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the bottom surface comprises one or more discontinuities.

Although supporting structure <NUM> has a bottom surface that is adjacent to build plate <NUM>, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which one or more portions of the bottom surface are not adjacent to the build plate.

Although supporting structure <NUM> has a top surface that is non-planar, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the top surface has any form (e.g., planar, irregular, convex, concave, hemispherical, etc.).

Although supporting structure <NUM> has a top surface that is continuous, it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which the top surface comprises one or more discontinuities.

In accordance with the illustrative embodiment, a length of filament is to be deposited and tamped onto the top surface of supporting structure <NUM>. In particular, the filament is to be deposited onto supporting structure <NUM> so that the longitudinal axis of the filament is to exactly coincide with a non-planar space curve called target path <NUM>. Because the filament has a circular cross-section and a diameter of <NUM>, target path <NUM> is represented parametrically by the vector function: <MAT> where: <MAT> <MAT> <MAT> wherein t is a real number in the range <NUM> ≥ t >_ <NUM>.

In accordance with the illustrative embodiment, target path <NUM> is a continuous non-planar curve, but it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention for any target path (e.g., straight, planar curve, non-planar curve, etc.).

In accordance with the illustrative embodiment, target path <NUM> does not comprise any discontinuities, but it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which a target path comprises one or more discontinuities.

<FIG>, and <FIG> depict orthographic front, side, and top views of tamping tool <NUM> in accordance with the illustrative embodiment. Tamping tool <NUM> comprises: tool shank <NUM>, wheel bracket <NUM>, wheel axle <NUM>, wheel bushings <NUM>, and wheel <NUM>. Wheel <NUM> is substantially symmetric around wheel axis <NUM>.

In accordance with the illustrative embodiment, tool shank <NUM>, wheel bracket <NUM>, wheel axle <NUM>, wheel bushings <NUM>, and wheel <NUM> are each fabricated from stainless steel, but it will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which any or all components are fabricated from a different material.

In accordance with the illustrative embodiment, the angular orientation of wheel <NUM> changes with respect to the coordinate system of additive manufacturing system <NUM> as it tamps filament <NUM>. In accordance with the illustrative embodiment, the angular orientation of wheel <NUM> is described in terms of three orthogonal axes:.

In accordance with the illustrative embodiment, the general convention for labeling the roll axis, pitch axis, and yaw axis for aircraft is not adopted for wheel <NUM> because the analogy is not perfect and might cause confusion when applied to wheel <NUM>.

In accordance with the illustrative embodiment, the pitch axis of wheel <NUM> is designated to be the axis - wheel axis <NUM> - around which wheel <NUM> exhibits substantial symmetry.

In accordance with the illustrative embodiment, the roll axis of wheel <NUM> is designated to be roll axis <NUM> (shown in <FIG>) because it is, in general, parallel to the direction of travel of wheel <NUM>. In accordance with the illustrative embodiment, roll axis <NUM> intersects wheel axis <NUM> but unlike an aircraft, is defined to remain horizontal (i.e., perpendicular to the Z-axis) and not incline or decline as wheel <NUM> rotates.

In the prior art, the yaw axis of wheel <NUM> is nip axis <NUM>, as shown in <FIG>, <FIG>, and <FIG> and described in detail below. In contrast, and in accordance with the illustrative embodiment, the yaw axis of wheel <NUM> is pinch axis <NUM>, as shown in <FIG>, <FIG>, and <FIG> and described in detail below.

<FIG> depicts an orthographic front view of tamping tool <NUM> along cross-section AA-AA in the context of tamping filament <NUM> onto supporting structure <NUM> along target path <NUM>.

In accordance with the illustrative embodiment, wheel <NUM> exerts different amounts of radial force on filament <NUM> at different places around its circumference. For example, touch line segment <NUM> is the line segment on the circumferential surface of wheel <NUM> at which wheel <NUM> initially touches a length of filament <NUM>. The radial force of wheel <NUM> on filament <NUM> at touch line segment <NUM> approaches zero.

In contrast, nip line segment <NUM> is the line segment on the circumferential surface of wheel <NUM> where wheel <NUM> exerts the maximum radial force on a length of filament <NUM>.

And in further contrast, pinch line segment <NUM> is the line segment on the circumferential surface of wheel <NUM> where wheel <NUM> first pinches a length of filament <NUM> between the circumferential surface and the supporting structure so that any movement of filament <NUM> parallel to wheel axis <NUM> is substantially constrained. It will be clear to those skilled in the art, after reading this disclosure, how to determine - both theoretically and empirically - the location of the pinch line segment for every embodiment of the present invention. Pinch line segment <NUM> is always between touch line segment <NUM> and nip line segment <NUM> on the circumferential surface of wheel <NUM>.

In both the prior art and in accordance with the illustrative embodiment, robot arm <NUM> tamps filament <NUM> onto supporting structure <NUM> by steering wheel <NUM> along target path <NUM>. There are significant differences, however, between how wheel <NUM> is steered in the prior art and in the illustrative embodiment. In the prior art, wheel <NUM> is steered along target path <NUM>:.

In accordance with the prior art, nip axis <NUM>:.

<FIG> depicts a top view of the relationship of supporting structure <NUM>, target path <NUM>, and filament <NUM> after filament <NUM> has been tamped by wheel <NUM> and steered using nip axis <NUM> as the yaw axis, as in the prior art. When nip axis <NUM> is used as the yaw axis for wheel <NUM>, wheel <NUM> has the detrimental effect of "trapping" the succeeding length of filament <NUM> off of target path <NUM> before it is "fixed" in place. In particular, when nip axis <NUM> is used as the yaw axis for wheel axis <NUM> , wheel <NUM> traps filament wide on curved portions of target path <NUM>. This is clearly disadvantageous.

In contrast, and in accordance with the illustrative embodiment, wheel <NUM> is steered along target path <NUM>:.

It will be clear to those skilled in the art, after reading this disclosure, how to make and use alternative embodiments of the present invention in which wheel <NUM> is steered in accordance with criteria i or ii or iii or any combination of i, ii, and iii.

In accordance with the illustrative embodiment, pinch axis <NUM>:.

The value of the offset s depends on the instantaneous curvature of target path <NUM> at pinch axis <NUM> with respect to pinch axis <NUM>. For example, the offset s has one value when target path <NUM> has no curvature (i.e., is rectilinear) as shown in <FIG>, a greater value when target path <NUM> is concave as shown in <FIG>, and a lesser value when target path <NUM> is convex, as shown in <FIG>. In accordance with the illustrative embodiment, the value of the offset s is adjusted dynamically as wheel <NUM> is steered along target path <NUM>. It will be clear to those skilled in the art, after reading this specification, how to determine - both theoretically and empirically - the value(s) for the offset s.

<FIG> depicts a top view of the relationship of supporting structure <NUM>, target path <NUM>, and filament <NUM> after filament <NUM> has been tamped by wheel <NUM> and steered using pinch axis <NUM> as the yaw axis, as in the illustrative embodiment. In accordance with the illustrative embodiment, the circumferential surface of wheel <NUM> precisely tamps filament <NUM> directly onto target path <NUM>, regardless of the curvature of target path <NUM> and supporting structure <NUM>.

<FIG> depicts a flowchart of the operation of the illustrative embodiment.

At task <NUM>, an engineer using computer-aided design software establishes a target path on a surface of supporting structure <NUM> where a segment of filament <NUM> should be deposited and tamped. It will be clear to those skilled in the art how to accomplish task <NUM>.

At task <NUM>, robot arm <NUM> and deposition head <NUM> - under the control of controller <NUM> - deposit a length of filament <NUM> along target path <NUM> on supporting structure <NUM>. It will be clear to those skilled in the art how to accomplish task <NUM>.

At task <NUM>, robot arm and tamping tool <NUM> tamp the length of filament <NUM> deposited along target path <NUM> onto in task <NUM>. Task <NUM> is described in detail in <FIG> and the accompanying text.

It will be clear to those skilled in the art that tasks <NUM> and <NUM> are performed concurrently on different lengths of filament <NUM>.

<FIG> depicts a flowchart of the details of task <NUM> - tamping filament <NUM> onto supporting structure <NUM> with tamping tool <NUM> by steering wheel <NUM> along filament <NUM>.

At task <NUM>, robot arm <NUM> and tamping tool <NUM> - under the control of controller <NUM> move wheel <NUM> so that the yaw axis - pinch axis <NUM> - intersects and advances along target path <NUM>. It will be clear to those skilled in the art, after reading this disclosure, how to make and use embodiments of the present invention that accomplish task <NUM>.

At task <NUM>, robot arm <NUM> and tamping tool <NUM> - under the control of controller <NUM> turn wheel <NUM> around the yaw axis - pinch axis <NUM> - to keep the roll axis - roll axis <NUM> - substantially parallel to target path <NUM> at the point where the yaw axis intersects target path <NUM>. It will be clear to those skilled in the art, after reading this disclosure, how to make and use embodiments of the present invention that accomplish task <NUM>.

Claim 1:
A method comprising:
depositing a filament (<NUM>) on a surface of a supporting structure (<NUM>) along a target path (<NUM>); and
tamping the filament onto the supporting structure with a wheel by steering the wheel along the filament;
wherein the wheel comprises:
(i) a pitch axis (<NUM>) around which the wheel is substantially symmetric; and
(ii) a circumferential surface that comprises:
(ii-a) a nip line segment (<NUM>) where the wheel exerts maximum radial force on a first length of the filament, and
(ii-b) a pinch line segment (<NUM>) where the wheel first pinches a second length of the filament between the circumferential surface and the supporting structure so that any movement of the second length of the filament parallel to the pitch axis is substantially constrained; and
(iii) a yaw axis (<NUM>) that:
(iii-a) is perpendicular to the pitch axis, and
(iii-b) has a non-zero offset s from the pitch axis, wherein s is a positive real number, and
(iii-c) intersects the pinch line segment; and
(iv) a roll axis (<NUM>) that intersects the pitch axis and the yaw axis and is perpendicular to the pitch axis and the yaw axis; and
characterized in that
steering the wheel comprises moving the wheel so that the yaw axis intersects and advances along the target path.