Method to improve fiber length measurement using confocal laser scanning microscope images

A method for measuring the lengths of industrial fibers is provided. The method employs the depth perception properties of a confocal laser microscope to monitor three-dimensional properties of the sample to determine fiber connectivity in areas where individual fibers in the sample overlap one another. This results in a more accurate matching of fiber termini in such situations, and obviates the need for algorithms which match fiber termini based on curvature, angle, or other two-dimensional properties.

TECHNICAL FIELD

The present invention relates in general to a method for measuring the lengths of industrial fibers in a sample.

BACKGROUND

It is very important to measure the length of fiber in polymers. Typically when analyzing a sample of fibers many of the individual fibers will overlap one another, making it difficult to determine which fiber termini belong to the same fiber and therefore difficult to confidently measure the lengths of individual fibers.

Confocal laser microscopes have the ability to analyze a microscopy sample in two-dimensions, but also to analyze a third dimension of depth, or distance between the sample and the microscope. In particular, a confocal laser microscope will give a differing signal intensity based on sample depth.

SUMMARY

A method for measuring fiber length in an industrial fiber sample is provided. The method includes a first step of providing an industrial fiber sample, the industrial fiber sample having at least two overlapping fibers, the at least two overlapping fibers defining an overlap region. The method includes a second step of measuring signal intensity within the overlap region using a confocal laser microscope. The method includes a step of distinguishing contiguous areas of signal intensity continuity from contiguous areas of signal intensity discontinuity and a step of identifying an individual fiber on the basis of these distinctions. The method finally includes a step of measuring the length of the identified individual fiber.

A system for automated measurement of fiber length is also disclosed. The system includes a confocal laser microscope positioned to direct confocal illumination at a sample analysis surface, and a controller configured to direct the confocal laser microscope to perform a two-dimensional sample scan, to detect an overlap region from the two-dimensional image data, and to direct the confocal laser microscope to perform a confocal intensity scan of the overlap region. The controller can employ an algorithm to automatically measure a fiber length based on the two-dimensional and confocal intensity data obtained.

DETAILED DESCRIPTION

Disclosed herein is a method for measuring the lengths of industrial fibers that are grouped in a sample in which different fibers are overlapping. The method is expected to be highly accurate and does not require elaborate algorithms used by other methods.

The disclosed method employs confocal laser microscopy to analyze fiber overlaps and thereby determine which pairs of fiber termini in an overlapping cluster belong together.

The term “fiber” as used herein refers to a flexible material of homogenous composition and thread-like shape. A fiber of the present disclosure will typically have a maximum dimension at or below the visibility limit to the human eye, for example a fiber length may range from about 100 μm to 2 mm. A fiber of the present disclosure will typically have a width or diameter in the range of one to fifty μm. In some instances, a fiber can have an aspect ratio in the range of 100 to 500.

The phrase “industrial fiber” as used herein generally refers to a synthetic or semi-synthetic fiber although natural fibers may also be used. Non-limiting examples of industrial fibers include cellulose, silicon carbide, organic polymer fiber, carbon fiber, and fiberglass. Industrial fibers are often used in meshed materials, woven materials, or as reinforcing elements of composite materials. In the last case, industrial fibers may be entrained in a polymeric matrix to enhance strength or alter other properties. In many industrial fiber deployments, it is desirable to know the lengths of industrial fibers in a sample, and length determination is often made by direct measurement with the assistance of magnification. Difficulty arises however when fibers in a sample are overlapped.

Referring now toFIG. 1A, first and second fibers10,12are shown at approximately 100× magnification. The first and second fibers10,12have fiber ends14a,14b,14c, and14d. While the first and second fibers10,12overlap one another, it may be difficult to tell by standard microscopy which of the first and second fibers10,12passes over the other in the direction of view. In addition, because the first and second fibers10,12have significant longitudinal alignment, it is difficult to correctly pair fiber ends14a,14b,14c, and14dand therefore difficult to measure the length of either of the first and second fibers10,12. For example, the first fiber10could include paired fiber ends14aand14cor it could include paired fiber ends14aand14d. An incorrect determination or guess of the paired fiber ends on fiber10would lead to an incorrect length measurement.

FIG. 1Bshows a recreation of a microscopic photograph of a fiber sample20, the image ofFIG. 1Bhaving about 50× magnification. It is to be understood that, in many instances, fiber sample20will be a sample of industrial fibers. Fiber sample20includes a first fiber22, a second fiber24, and a third fiber26, each of the first, second, and third fibers22,24,26passing through an overlap region28.

A fiber sample20such as that shown inFIG. 1Bcan be obtained prior to deployment of the fibers in a material, or can include fibers recovered from a deployed material. For example, industrial fibers deployed in a composite material can frequently be recovered by removing the polymeric matrix, for example by burning, melting, or dissolving the polymeric matrix, depending on the combustion temperatures, melting temperatures, or solubilities of the fibers and polymeric matrix.

FIG. 2Ashows an overhead view of an overlap region28of an industrial fiber sample having fibers22,24,26.FIG. 2Bshows a side view of the overlap region28with a confocal laser microscope50positioned above. As should be understood, the overlap region28can vary in size and shape based on the particular fibers and their spatial arrangement. Due to the ability of the confocal laser microscope50to measure signal intensity based on distance between the microscope and sample region, or sample depth, the confocal laser microscope50is able to provide data suitable to determine fiber connectivity for each of the three fibers22,24,26. Thus, it is possible to determine, in the example ofFIG. 2B, that fiber22overlaps fiber24and that fiber24overlaps fiber26, based on signal intensity. This then allows for matching of fiber termini by monitoring fiber connectivity across the length of each fiber22,24,26.

While the confocal laser microscope50utilized in the method100can utilize fluorescence confocal microscopy to analyze the fiber sample20, for example by attaching fluorophores to individual fibers, it is anticipated that reflection confocal microscopy will be frequently utilized. The confocal laser microscope50can in some implementations be utilized for two-dimensional scanning of the fiber sample20as well as depth determination within the at least one overlap region28.

Referring now toFIG. 3, a method100for measuring the lengths of individual fibers includes a first step101of providing a fiber sample, such as a fiber sample20. The fiber sample20will typically have at least two fibers, such as first, second, and third fibers22,24,26that define an overlap region28.

In a second step102of method100, and with continued reference toFIGS. 2A and 2B, signal intensity is measured in an area adjacent to and/or within the overlap region28using a confocal laser microscope50. The confocal laser microscope can focus illumination light at a point in a focal plane such that intensity of detected light (e.g. reflected or fluoresced light) will be proportional to the proximity of the reflecting or fluorescing sample surface to the focal plane. Thus, the confocal laser microscope50can be focused at a focal plane parallel to and located some distance, such as an average cross sectional diameter of fibers, above a surface on which the industrial fiber sample is supported. Any fiber surfaces located above or below the focal plane (i.e. nearer or farther, respectively to the confocal lens than is the focal plane) will produce a weaker detectable signal than those surfaces located at the focal plane. For example, and with specific reference toFIG. 2A, overlapping fiber22can have a signal intensity at points distant from fibers24and26if the focal plane is a fiber diameter above the supporting surface, but the signal intensity will be lower at points on fiber22where fiber22is resting on top of fibers24and26such that fiber22is above the focal plane at those points. Fiber26can have a consistently high signal intensity across its entire length, except where it is covered by fiber22and/or fiber24.

In a third step103of method100, contiguous areas of signal continuity and contiguous areas of signal discontinuity are distinguished within the overlap region28. In general terms, “contiguous areas of signal continuity” refers to a portion of the overlap region in which signal intensity is uniform or changes only gradually, whereas “contiguous areas of signal discontinuity” refers to a portion of the overlap region within which there is a relatively abrupt difference in signal intensity. In more specific terms, “contiguous areas of signal continuity” can comprise two points within an overlap region28, the two points spatially separated by no more than a specific distance (a “contiguity distance”) and having a signal intensity difference not greater than a defined amount (an “intensity continuity threshold”). Distinction between contiguous areas of signal continuity and contiguous areas of signal discontinuity can be made by a user through visual examination, or by a controller apparatus operating an algorithm.

In implementations wherein the distinguishing step103is performed by a controller apparatus operating an algorithm, the method100can include additional steps of designating an absolute intensity threshold, defining an intensity continuity threshold, and setting a contiguity distance. The absolute intensity threshold is a minimum signal intensity to be applied at the measuring step102, such that a portion of the overlap region28having signal intensity less than the absolute intensity threshold can be ignored in the distinguishing step103. As mentioned above, the intensity continuity threshold is also an intensity value that can be employed in the distinguishing step103. Contiguous areas having a signal intensity difference less than the intensity continuity threshold can be distinguished as contiguous areas of intensity continuity, while contiguous areas having an intensity difference greater than the intensity continuity threshold can be distinguished as contiguous areas of intensity discontinuity. Also, as mentioned above, the contiguity distance is a value having units of distance and can be used to define whether areas are contiguous. Two points separated by a distance less than the contiguity distance can be deemed contiguous areas, while two points separated by a distance greater than the contiguity distance can be deemed not contiguous.

The method100can include an additional step104of identifying an individual fiber within the overlap region, on the basis of the distinction between contiguous areas of intensity continuity or discontinuity. In one implementation, an individual fiber can be identified as a fiber occupying only contiguous areas of signal intensity continuity. In another implementation, an individual fiber can be identified as a fiber occupying contiguous areas of signal intensity continuity interrupted by a contiguous area of signal intensity discontinuity.

Referring again toFIG. 2A, first fiber22can be identified as an individual fiber based on its occupancy only of contiguous areas of signal intensity continuity. Second fiber24can be identified as an individual fiber based on the fact that the signal intensities of its portions on either side of the crossing junction are continuous with one another, but are interrupted by the short signal intensity discontinuity of overlapping first fiber22.

In another step105of the method100, the length of the identified individual fiber is measured. In general terms, an individual fiber can be identified in step104by the individual fibers occupancy of contiguous areas of signal intensity continuity. For example, an individual fiber which lies across the top (i.e. nearest the confocal laser microscope50) of an overlap region28, such as overlapping first fiber22ofFIG. 2A, the individual fiber can be identified by occupancy only of contiguous areas of signal intensity continuity. In such an instance, the maximum linear or curvilinear length of contiguous areas of signal intensity continuity can represent the length of the individual fiber.

In some instances, an individual fiber can be identified in step104by the individual fibers occupancy of interpolated contiguous areas of signal intensity continuity.FIG. 4illustrates an example in which identification of an individual fiber based on occupancy of interpolated contiguous areas of signal intensity continuity can be accomplished.FIG. 4shows an overlap region28wherein a lower (i.e. farther from the confocal laser microscope50) fiber30is overlapped with an upper (i.e. nearer to the confocal laser microscope50) fiber31. Lower fiber30occupies a first region30A of contiguous areas of signal intensity continuity and a second region30B of contiguous areas of signal intensity continuity, but the complete contiguous areas of signal intensity continuity of lower fiber30are interrupted by upper fiber31, and in particular by contiguous areas of signal intensity discontinuity bounding the interrupting region31A. In such a scenario, lower fiber31can be identified as an individual fiber in step104through a process of extrapolation and/or interpolation. For example, beginning at the point at which the first region30A contacts the interrupting region31A, signal intensity continuity can be extrapolated in the direction of the arrow a. If the region of extrapolated signal intensity values encounter a matching region of detected contiguous areas of signal intensity continuity, such as in the second region30B, then the individual fiber30can be identified as including the first region30A and the second region30B. As will be obvious to one skilled in the art, such an extrapolation and/or interpolation analysis can be performed in either direction, or bi-directionally. In some variations, matching of extrapolated and/or interpolated signal intensity continuity with a region having detected contiguous areas of signal intensity continuity can include an error margin. Such an error margin can be termed an “interpolation margin”. In some variations, extrapolation and/or interpolation of signal intensity continuity can be limited to a maximum distance. Such a maximum distance can be termed an “interpolation distance”. In some variations, determination of interpolated contiguous areas of signal intensity continuity may be performed only if interrupting region (e.g.31A) has signal intensity greater than the absolute intensity threshold.

Also disclosed is a system for automated measurement of fiber length. The system can include a sample analysis surface and a confocal laser microscope50positioned to focus an illumination beam at a focal plane positioned at or adjacent to the sample analysis surface. The system can optionally include a controller configured to automate two-dimensional scanning of a fiber sample20placed on the sample analysis surface. In some implementations, the controller can be configured to identify an overlap region28. In such implementations, the controller can then perform steps102,103,104, and105of the method100as described above to measure the length of a fiber in the overlap region28. The controller can make use of an algorithm which employs an absolute intensity threshold, an intensity continuity threshold, and/or a contiguity distance, as disclosed above.

FIG. 5provides additional steps such as in a method200for measuring industrial fiber length. The method200is based on the method100, but may be useful for adaptation to an automated system for measuring fiber length. In a first step201, a sample of industrial fibers20is spread on a sample analysis surface, either by a user or by an automated/robotic assembly. In steps202/203, a controller directs a confocal laser microscope50to perform a two-dimensional scan of the fiber sample20, the controller subsystem detecting an overlap region28from the two-dimensional image data. In steps202/204, the controller directs the confocal laser microscope to perform a confocal intensity scan of the overlap region28. In step205, the controller uses an algorithm to distinguish contiguous areas of signal intensity continuity from contiguous areas of signal intensity discontinuity; to identify and individual fiber within the overlap region; and to measure the length of the identified individual fiber; as disclosed above.

The foregoing description relates to what are presently considered to be the most practical embodiments. It should be understood that in the discussion of various methods having a number of steps, the disclosed steps can be performed independently or can be combined. In addition, the discussion of steps in a particular order is not intended to imply limitation to any chronological order. It is to be understood that the disclosure is not to be limited to specific examples discussed but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.