Height control and deposition measurement for the electron beam free form fabrication (EBF3) process

A method of controlling a height of an electron beam gun and wire feeder during an electron freeform fabrication process includes utilizing a camera to generate an image of the molten pool of material. The image generated by the camera is utilized to determine a measured height of the electron beam gun relative to the surface of the molten pool. The method further includes ensuring that the measured height is within the range of acceptable heights of the electron beam gun relative to the surface of the molten pool. The present invention also provides for measuring a height of a solid metal deposit formed upon cooling of a molten pool. The height of a single point can be measured, or a plurality of points can be measured to provide 2D or 3D surface height measurements.

BACKGROUND OF THE INVENTION

Electron beam freeform fabrication (EBF3) is a manufacturing deposition process in which an electron beam is used in conjunction with a wire feed to progressively deposit material onto a substrate in a layered manner. The electron beam is translated with respect to a surface of the substrate while the wire is melted and fed into a molten pool. In an EBF3process, a design drawing of a three-dimensional (3D) object can be sliced into different layers as a preparatory step, with the electron been tracing each of the various layers within a vacuum chamber. The layers ultimately cool into a desired complex or 3D shape.

Taminger U.S. Patent Publication No. 2010/0260410 discloses a closed-loop control method and apparatus for an electron beam freeform fabrication (EBF3) process. The method of the '410 application can include use of one or more algorithms that are executed via a host machine of the apparatus set forth in the Taminger '410 application. The method uses a sensor or sensors to automatically detect or measure features of interest in the EBF3process, e.g., by imaging molten pool during the EBF3process. Detecting/measuring can be accomplished utilizing cameras, thermal sensors, and/or other suitable means. Sensor data describing the features of interest is fed into the host machine, which evaluates the sensor data to detect a magnitude/degree and/or a rate of change in the features of interest. The algorithm generates a feedback signal which is used by the host machine to modify a set of input parameters to the EBF3process.

The Taminger '410 application discloses a closed-loop control method for an EBF3process wherein a wire is melted and progressively deposited in layers onto a suitable substrate to form a complex product. The method includes detecting or measuring a feature of interest of the molten pool during the EBF3process using at least one sensor, continuously evaluating the feature of interest to determine, in real time, a change occurring therein, and automatically modifying a set of input parameters to the EBF3process to thereby control the EBF3process.

The Taminger '410 patent publication also discloses an apparatus that provides closed-loop control of the EBF3process, with the apparatus including an electron gun adapted for generating an electron beam, and a wire feeder for feeding a wire toward a substrate where the wire, once melted into a molten pool by the beam, is progressively deposited into layers onto the substrate. The apparatus also includes a host machine and at least one sensor. The sensors are adapted for detecting or measuring a feature of interest of a molten pool formed during the EBF3process, and the host machine executes one or more algorithms to continuously evaluate the feature of interest and determine, in real time, a change occurring therein. The host machine automatically modifies a set of input parameters to the EBF3process, i.e., by signaling a main process controller to change one or more of these parameters, to thereby control the EBF3process in a closed-loop manner.

As discussed in the Taminger '410 patent publication, a sensor in the form of a side-view optical camera can be used to monitor the height of a deposited bead on a substrate, and the distance between the deposited bead and the wire feeder. In such an embodiment, cross-hairs may be superimposed over the optical image, with the z-height of the deposit adjusted up or down to maintain the height of the current deposited layer centered on the cross-hairs.

During known EBF3processes, a human operator sets the height of the electron beam gun relative to the substrate. To initiate the start of a new layer the operator estimates visually where the wire should be in reference to the height of the previous deposit. If, because of a had estimation or a love spot in the previous layer, the feed height becomes too high, drips can result and the operator must input a command to lower the height of the electron beam gun and wire feeder. If the estimation is too low the feed wire can scrape against the previous deposit and can be forced out of the molten pool. In some cases, the misaligned wire can fuse with the previous deposit near the molten pool and cause a “wire stick.” In that case the deposition process must be halted so that the wire can be cut away from the deposition.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present disclosure is a method of controlling a height of an electron beam gun and wire feeder during deposition of layers of molten matter onto a substrate in an electron beam freeform fabrication process. The molten pool has a surface at an actual distance from the electron beam gun. The method further includes utilizing a camera to generate an image of the molten pool of material. A range of acceptable heights of the electron beam gun is determined, and the image generated by the camera is utilized to determine a measured height of the electron beam gun relative to the surface of the molten pool. The method further includes ensuring that the measured height is within the range of acceptable heights of the electron beam gun relative to the surface of the molten pool.

DETAILED DESCRIPTION

An apparatus10(FIG. 1) of the type described in more detail in U.S. Patent Publication No. 2010/0260410, and U.S. Pat. No. 7,168,935 the contents of each being incorporated, by reference in their entirety, is configured for use in an electron beam freeform fabrication process, hereinafter abbreviated as EBF3for simplicity. An example of an EBF3process to which the present disclosure could be applied is also described and claimed in U.S. Pat. No. 7,168,935. As will be understood by those of ordinary skill in the art, an EBF3process allows a complex object, e.g., a vehicle, aircraft, or spacecraft component, to be formed in a progressive or layered manner using an electron beam14. The apparatus10is used with an EBF3process, and includes an electron beam gun12contained in a sealed container or vacuum chamber50capable of maintaining a controlled atmosphere. The controlled atmosphere can comprise a vacuum or a suitable gas or mixtures of gasses. The gun12, part of which can be positioned outside of the chamber50for access and electrical connectivity, is adapted to generate and transmit an electron beam14within the controlled atmosphere, and to direct the beam toward a substrate20. In the embodiment ofFIG. 1, the substrate20is positioned on a moveable platform21. Alternately, the gun12can be completely enclosed within chamber50so that the gun is also moved rather than just the substrate20. In either embodiment, the gun12moves relative to the substrate20. It will be understood that the processes herein can, when discussing relative movement, simply refer to movement of the gun in the written description and/or claims. This movement, unless expressly stated otherwise, can actually comprise movement of both the gun and the substrate20, or movement of only the gun or substrate.

The platform21and/or the gun12may be movable via a multi-axis positioning drive system25, which is shown schematically as a box inFIG. 1for simplicity. A complex or three-dimensional (3D) object is formed by progressively forming and cooling a metal deposit in the form of a molten pool24into layers29on the substrate20. Metal deposit24is initially in the form of a molten pool that is formed by beam-melting of consumable wire18, e.g., a suitable metal such as aluminum or titanium, which is fed toward the molten pool from a wire feeder16. The term “metal deposit” is used herein if the metal is in a solid state, and the term “molten pool” is used herein if the metal is in a liquid state. Wire feeder16can comprise a spool or other suitable delivery mechanism having a controllable wire feed rate or speed. While not shown inFIG. 1for simplicity, chamber50can be evacuated using a vacuum subsystem such as a turbo-molecular pump, a scroll pump, an ion pump, ducts, valves, etc., as understood in the art.

The apparatus10also includes a closed-loop controller (C)22having a host machine27and an algorithm(s)100adapted for controlling an EBF3process conducted using the apparatus. Controller22is electrically connected to or in communication with a main process controller (Cm)30which, as understood in the art, is adapted for sending necessary commands to the gun12, the wire feeder16, and any required motors (not shown) that position the substrate20and the gun. The commands include a set of final control parameters11F. The controller22generates and transmits a set of input parameters11that modifies the final control parameters11F.

The wire18, when melted by the electron beam14, e.g., to over approximately 3000° F. in one embodiment, is accurately and progressively deposited, layer upon layer, according to a set of design data19, e.g., Computer Aided Design (CAD) data or another 3D design file. In this manner, a 3D structural part or other complex object can be created in an additive manner without the need for a casting die or mold. This provides for rapid prototyping and hands-free manufacturing of vehicle, airplane, spacecraft, and/or other complex components or parts.

In order to achieve closed-loop EBF3process control, the closed-loop controller22ofFIG. 1can be electrically connected to one or more sensors (S)15to detect or measure one or more specific features of interest of the molten pool24, with the information describing the feature of interest relayed to the controller22as a sot of sensor data13. Host machine27receives the sensor data13and runs one or more algorithms, represented collectively as the algorithm100inFIGS. 1 and 2, to interpret the sensor data. The controller22signals the main process controller30to modify the final control parameters11F for the EBF3process as needed. For example, the controller22can signal the main controller30to alter a feed rate of the wire feeder16, a power value of the gun12, a speed of the moveable platform21, and/or any other components of the apparatus10.

Host machine27can comprise a desktop computer equipped with a basic data acquisition and analysis software environment, e.g., Lab View® software, and high speed data acquisition boards for real-time acquisition and analysis of large volumes of data associated with high speed data images. The host machine27can include sufficient read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), etc., of a size and speed sufficient for executing the algorithm100as set forth below. The host machine27can also be configured or equipped with other required computer hardware, such as a high speed clock, analog-to-digital (A/D) and digital-to-analog (D/A) circuitry, input/output circuitry and devices (I/O), as well as appropriate signal conditioning and/or buffer circuitry. Any algorithms resident in the host machine27or accessible thereby, including the algorithm100as described below, can be stored in memory and automatically executed to provide the respective functionality.

Algorithm100is executed by the host machine27to interpret the sensor data13, and to assess the magnitude and speed of any changes occurring during the EBF3process. As discussed in more detail in the Taminger '410 patent publication, a closed feedback loop is formed between the controller22, working with the main process controller30and the controlled EBF3system components, e.g., the electron gun12, wire feeder16, etc., to allow for a real-time modification to the final control parameters11F.

The features of interest to be monitored during the EBF3process are measured/determined by the sensors15. Sensors15can comprise a charge-coupled device (CCD)-equipped camera adapted to convert an image of the process region (arrow A) into a digital signal suitable for processing by the host machine27. Sensors15can also include a Complementary Metal-Oxide Semiconductor (CMOS)-based camera used to visually monitor the EBF3process with relatively low noise/low power consumption. Sensors15can use a CCD-equipped camera in conjunction with an infrared (IR) band-pass filter(s) to thermally image the EBF3process. A secondary electron detector can also be used as or with one of the sensors15to further visually monitor the EBF3process.

As shown inFIG. 1, at least one of the sensors15can be mounted outside of the vacuum chamber50, e.g., when a fixed-gun system is used. As will be understood by those of ordinary skill in the art, in a fixed-gun system all motion occurs on the deposited part such that the deposition process always occurs in the same spot, thereby enabling installation of a sensor15in the form of a fixed camera at a position outside of the vacuum chamber50. A sensor15configured and positioned as described can be used to monitor, for example, a height of any deposited material or bead of the molten pool24, and/or a distance between the molten pool and the wire feeder16.

Sensors15equipped as digital cameras having CCD capability can be installed in several different orientations inside the process chamber50, with the digital cameras being focused on the process zone as indicated by arrow A. A CMOS-equipped camera can be installed outside of the vacuum chamber of gun12, and a fiber optic cable (not shown) or other communications conduit can be used to transmit images from within the vacuum chamber to the CMOS camera. These cameras can be used to image bead shape and height during formation of the molten pool24, a location of the wire18relative to the molten pool, and melt pool shape and area as determined by examining the change in reflectance between the molten and solid material.

IR band-pass filters may also be installed on sensors15configured as CCD-equipped or CMOS-equipped digital cameras in order to examine a temperature of the molten pool24and the surrounding region. A secondary electron detector as noted above can be installed and adapted to use electrons from the electron beam14to image the EBF3process in real-time. Electrons reflected off wire18and the molten pool24can be pulled into a sensor15adapted as such a secondary electron detector to provide an image of anything that the incident electron beam encounters. A raster pattern of the electron beam14can be automatically modified to expand the imaging field. It will be understood that various imaging devices can be utilized, and the present invention is therefore not limited to specific imaging devices, CCD and CMOS.

As discussed above, during known prior EBF3processes, a human operator sets the height of the electron beam gun relative to the substrate. One problem with this approach is that for deposition consistency from layer to layer, the working height should stay within a known “good” range. Although the height of the electron beam gun relative to the substrate can be measured utilizing known sensors, variations in the thickness of the layers of material and variations in the thickness of the pool of material create difficulties with respect to accurately determining the distance between the electron gun and the surface of the molten pool. Still further, a lack of automation can lead to increased operator work-load and training. Also, a lack of automation typically prevents an operator from leaving the process unattended in an industrial setting.

Automation of the height control aspect of the process can be accomplished utilizing a video camera15A (FIG. 2), image processing, and communication with the EBF3's control system described above. With further reference toFIG. 3, camera15A is initially positioned with the worksurface area5within the field of view of camera15A as shown at34inFIG. 3. In general, the worksurface area5comprises the area on substrate20within which the molten pool of material24is formed. The line of sight6of camera15A forms an angle θ relative to substrate20. The angle θ remains constant as the vertical position of substrate20is changed/adjusted. A structure32interconnects the electron beam gun12, camera15A and wire feeder16, such that the positions of the electron beam gun12, camera15A, and wire feeder16do not change relative to one another. After the camera15A is positioned, a calibration step36is performed to establish the relationship between the camera15A and the working height “H”, which is the distance between the EBF3gun12and the working surface or substrate20. A target dot8will appear to move in the camera's field of view as the working height is varied as designated “H1.” This is due to the angle θ of the line of sight6of camera15A. The angle θ need not be measured utilizing the procedure of the present invention.

Calibrating the system includes setting the EBF3working height H, and establishing this as the zero height for the EBF3robotics at step36A. Once the zero height is established, a line9representing the electron beam14intersects a line4of wire18along substrate20and the plane38of worksurface or substrate20. Once the zero height is established, a target dot8is placed in the view of the camera15A. The dot is initially positioned at the X, Y, Z coordinates of [0.000, 0.000, 0.000]. For a 5-point calibration the working height may be set to −0.050, −0.025, 0.000, 0.025, and 0.050 inches at step36B. It will be understood that these are example heights, and a broader or narrower range or different numbers of calibration points may be acceptable.

The change of location of the target dot8can be utilized to develop a mathematical relationship between the pixel location verses the height of the camera. The pixel location of the target dot8will change on the Y-axis of the camera image as the camera15A changes location vertically as shown by the dimension “H1” ofFIG. 2. A plot of the pixel location verses the height of the camera15A results in a straight line representing the pixels per inch. Later, during the deposition process, the centroid of the molten pool24can be used to estimate an error from the ideal build height. For example, if the pixel location verses the height of the camera results in an equation of the form y=mx+b, the constant “m” can be determined from the line correlating pixel location verses height of the camera (i.e. m=y/x if b=0). The measured height will then be equal to y/m, where y is equal to the centroid of the molten pool24. From this, an error correction may be generated and sent to the EBF3system to alter the working height H. Since the molten pool24has a thickness, the ideal working height can be an offset from what has been calibrated as 0.000 inches.

Also, since the height H is controlled and monitored by the control system, it is possible to predict the height setting at which to start the next layer of deposition. This should be an offset value that will depend on the material being deposited and at the rate at which the material is deposited. Wire feed rate, travel speed, and electron beam energy will typically affect the thickness of the deposition. In a similar fashion, an array of target dots can be printed on a target in a square grid pattern of known size. The pattern of dots will displace on the Y-axis in the camera view as the working height H is changed. At each measurement height, similar to the straight-line pixels/height above, a correction factor can be computed for each square in the camera's view, and a calibration table can be constructed.

It can be that for small changes in height the areal correction is too small to be relevant. Thus, the technique is possible, but it may not be necessary in every case.

In addition to measurement of a working height of electron beam gun12relative to a molten pool24to provide closed loop control of the EBF3process, the present invention also provides for use of electron beam gun12to measure the height of a solid (cooled) metal deposit24. This eliminates the need for a separate laser-based height measurement system (not shown) as used in known systems/processes. In existing systems, the deposition height of a solid metal deposit24can be measured utilizing a separate point laser system. In these existing systems, the measuring unit shines a point of laser light at the target and a sensor in the unit receives the reflected light. Triangulation is used to estimate the distance from the sensor to the reflecting target. This type of laser-based system works well to measure the height of an aluminum deposit because the surface finish of the aluminum is reflective but not shiny. However, titanium has a very shiny surface and laser systems may not provide accurate measurements. In some laser measurement applications, a powder is applied to the shiny surface to reflect a suitable image of the laser dot. However, in the EBF3system described above, use of powder is not a viable option due to difficulty involved in applying the powder in the vacuum systems. Also, the powder can have a negative effect on the next deposit layer.

To measure the height of a solid metal deposit24, electron beam14is set to a low power level that produces a visible dot on metal deposit24without melting deposit24. The calibration curve (e.g. straight line of a form y=mx+b) discussed above can then be used to estimate or measure the height. For this type of measurement, the electron beam14is energized just enough to create a hotspot on the target that is bright enough for the camera15A to capture accurately. This results in more energy entering the metal deposit24. Excessively high beam energy could alter the desired mechanical properties. However, once the minimum power settings and/or beam focus settings are established, this method is suitable for any metal target. Use of the electron beam gun12to measure the height of solid metal deposits eliminates the need for a separate laser-based height measurement system.

In addition to the “single point” height measurement of a metal deposit24described above, the camera15A can also be utilized to measure a plurality of heights along a line to thereby measure a surface contour line52(FIG. 4) of a metal deposit24that has been formed on a substrate. A plurality of 2D surface contour lines52can be measured to thereby determine a 3D contour of the surface of a metal deposit24. As discussed in more detail below, measuring the surface contour line52of a metal deposit24involves generating a low power beam14that is deflected in an oscillating manner such that a line is projected on the substrate. It will be understood that existing electron beam guns12include beam deflection features that permit control of the direction of electron beam14. During measurements and/or calibration, electron beam gun12can be adjusted to provide a low power beam that generates a visible spot on the target surface that can be captured in a digital image by camera15A (FIG. 2) without transferring significant amounts of energy into the target surface.

2D calibration can be accomplished by positioning three dots8A,8B, and8C on substrate20. The dots8A,8B, and8C can comprise black dots positioned on a white sheet of paper or other planar substrate. It will be understood that the line50does not necessarily need to be drawn on the sheet of paper, and line50is shown inFIG. 4for discussion purposes. In general, the electron beam gun12can deflect the beam14to travel along a line that is on the order of 0.5 inches to as long as 2.0 inches. These dimensions are examples of the capability of known electron beam guns12. However, the present disclosure is not limited to these specific examples. The dots8A,8B, and8C are positioned such that the line50is parallel to the X axis of the system (see alsoFIG. 2). Dot8B is located between dots8A and8C, and dots8A and8B are spaced from dot8A by distances “L1” and “L2”, respectively. The distances L1and L2are preferably equal to one another such that dot8B is centered between dots8A and8C. The distance between the dots8A and8C is “L”, in general, the length L is selected to correspond to the maximum deflection angle of electron beam14that can be generated by electron beam gun12. The center dot8B is positioned such that it is directly at a point where a non-deflected beam14would pass. With the electron beam gun12set to its normal working distance H (FIG. 2), this point is at the Z=0 plane in the coordinate system of the apparatus10. As discussed above, the dots8A,8B, and8C are parallel to the axis X. The line50is therefore perpendicular to the line of sight6of camera15A (FIG. 2).

The 2D calibration of points8A,8B, and8C is similar to the “1D” calibration procedure discussed above in connection withFIGS. 2 and 3. The working height H is established as the zero height for the EBF3robotics as shown at step36A (FIG. 3). Dot8B is initially at the X, Y, Z coordinates of [0.000, 0.000, 0.000]. The lengths of the lines L1and L2are known, such that the dot8A is initially at the XYZ coordinates of [−L1, 0.000, 0.000], and dot8C is initially at the XYZ coordinates of [L2, 0,000, 0.000]. The electron beam gun12is then moved through a series of predefined working heights (e.g. −0.050, −0.025, 0.000, 0.025, and 0.050, as discussed above) relative to the substrate20. As the height of the camera15A changes relative to the substrate20, the digital images (pixels)8A′,8B′, and8C′ of dots8A,8B, and8C, respectively, change positions by an amount “H2”. The dimension H2inFIG. 4corresponds to the Y axis of the camera image. At each height setting the positions of the dots8A,8B, and8C arc recorded by imaging software.

Two calibrations can be computed from these images. First, a relationship between the positions of the images8A′,8B′, and8C′ to an actual height is determined. For example, the actual heights of the points8A,8B, and8C relative to the positions of the images8A′,8B′, and8C′ can be in the form of an equation y=mx+b. Once the relationship (e.g. an equation y=mx+b) between the actual heights and the positions of the images is determined, the positions of images8A′,8B′, and8C′ can be utilized to calculate a measured vertical position of points on a surface of metal deposit24in use. During measuring operations the electron beam gun12can be set to a low power setting that does not introduce significant energy levels into metal deposit24, and the electron beam14can be oscillated to provide a plurality of images (i.e. pixels) along line50.

It will be understood that additional dots can be positioned between the dots8A,8B, and8C during the calibration process such that, a relationship between the image location and actual height can be determined for a large number of points along line0. Thus, in use, the heights at a large number of positions58A-58G along a surface contour line50can be measured/determined in use. A best fit line can then be calculated to provide a surface contour line52of the metal deposit24at a specific Y coordinate. Additional measurements can be taken at a plurality of Y positions to provide additional surface contour lines52of the metal deposit24.

In addition to the height calibrations and measurements discussed above, a second calibration and measurement can be utilized to determine the lateral locations of the positions/dots58A-58G on a surface contour line52. The lateral locations of the positions/dots or58A-58G can be determined relative to a center line C passing through the center location (point8B). Determining the lateral locations of the points58A-58G requires a second calibration. As discussed above, the dots8A,8B, and8C can be moved to a plurality of known heights, and the relationship between the changes in position in the camera image and the heights can be determined. Using the image taken at the Z=0.0 position, the number of pixels between the dots8A and8C and the center dot8B in the camera image can be counted. The distances L1and L2are known, and these distances can be divided by the number of pixels in the distances to establish a relationship between the observed pixel location in the camera image and a physical location on the target or substrate. The number of pixels in each image corresponding to the calibration heights can be utilized to provide a relationship between the number of pixels and the lengths L1and L2at each calibration height. Additional dots (not shown) between dots8A-8C can be utilized during the calibration process to establish a relationship between the image locations and the lateral positions of the additional dots. These calibration points can then be utilized to determine the distances from centerline C to positions58B-58F on surface contour line52.

Alternately, calibration for the points58B-58F can be estimated from the calibration relationship for the outer points8A and8C. For example, if points58A-58D are equally spaced apart, the lateral distances between points58A and58B will be L1/3, the distance between points58B and58C will also be L1/3, and the lateral distance between points58C and58D will also be L1/3. As discussed above, the length L1is divided by the number of pixels N to establish a relationship between the observed pixel location in the camera image and a physical location. For the point8A, at a given calibration height this relationship would be L1/N. For the point58B, the estimated lateral distance relationship would be 2(L1)/3N, and the estimated relationship for the point58C would be L1/3N.

In use, capturing a profile line52is a 2D measurement. 3D topography can be measured by moving the line resulting from oscillation of beam14around the metal deposit24and the component that is being formed utilizing the EBF3process.

As discussed above, the calibration can be conducted at a plurality of discreet heights, both negative and positive, about a 0.000 working height. In use, measurements are preferably made as close as possible to the 0.000 working height. For example, a first bead or layer can be deposited and measured as the system is moved in the Z=0.000 plane. Measurements from the image processing will be relative to the initial substrate, and therefore need no adjustment. If the first layer has a height of 0.025 inches, then the second deposit or layer would be measured as the robotics travel in the Z=0.025 inches plane. Measurements from the imaging system will then have 0.025 inches added to them to account for the Z displacement of the robotic system.

Since the camera15A (FIG. 2) is at an angle θ relative to the plane of the part being built, there may be a shadow area that the camera15A cannot image, and the heights in the shadow area cannot therefore be measured. Accordingly, the substrate20is preferably rotatable about the Z axis, or the camera15A can be rotatable about the part being made. The camera15A can thereby generate images that can be utilized to measure the contours/heights of the component in the areas that would otherwise not be imagable by camera15A.

Although the system has been described as having a single camera15A, an additional camera15A can be positioned on an opposite side of electron beam gun12, and stereoscopic methods can be utilized to make height measurements. Additional cameras15A could also be positioned about the component/molten pool/metal deposit24to provide for more accurate or more detailed measurements. For example, with reference toFIG. 2, cameras15A could be positioned at locations along the Y axis, and at a −Y axis location, and cameras15A could also be positioned along the +X axis and the −X axis.

All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. Each range disclosed herein constitutes a disclosure of any point or sub-range lying within the disclosed range.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As also used herein, the term “combinations thereof” includes combinations having at least one of the associated listed items, wherein the combination can further include additional, like non-listed items. Further, the terms “first,” “second,” and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity).

Reference throughout the specification to “another embodiment”, “an embodiment”, “some embodiments”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and can or cannot be present in other embodiments. In addition, it is to be understood that the described elements can be combined in any suitable manner in the various embodiments and are not limited to the specific combination in which they are discussed.