Apparatus and method for measuring haze of sheet materials or other materials

A method includes illuminating a material with first light and capturing an image of second light transmitted through the material. The method also includes analyzing multiple regions of the image and determining one or more haze measurements associated with the material based on the analyzing. The method further includes storing and/or outputting the one or more haze measurements. Analyzing the multiple regions of the image may include summing pixel values in each region to produce a total pixel value for that region. The multiple regions of the image may include (i) a first region forming a first disc, (ii) a second region forming either a first annular region around the first region or a second disc larger than and including the first disc, and (iii) a third region forming either a second annular region around the second region or a third disc larger than and including the first and second discs.

TECHNICAL FIELD

This disclosure relates generally to measurement systems and more specifically to an apparatus and method for measuring haze of sheet materials or other materials.

BACKGROUND

Many transparent, translucent, or other non-opaque materials are produced in long webs or sheets. One characteristic of these types of materials is haze, which refers generally to the scattering of light passing through the materials. Haze typically reduces the contrast of objects viewed through the materials. For example, haze in a plastic sheet used in product packaging might reduce the clarity of lettering viewed through the plastic sheet. Low haze may be important or essential for certain applications, such as consumer electronics packaging or medical device packaging.

Haze measurements typically occur in laboratory settings. For example, a sample of a material can be positioned against an entrance port of an integrating sphere, which can measure the haze of the sample. However, conventional laboratory instruments for measuring haze are typically not suitable for use in a manufacturing or processing environment. Moreover, conventional laboratory instruments for measuring haze are typically contact-type devices, meaning the devices must be placed in physical contact with a material.

SUMMARY

This disclosure provides an apparatus and method for measuring haze of sheet materials or other materials.

In a first embodiment, a method includes illuminating a material with first light and capturing an image of second light transmitted through the material. The method also includes analyzing multiple regions of the image and determining one or more haze measurements associated with the material based on analyzing the multiple regions. The method further includes storing and/or outputting the one or more haze measurements.

In a second embodiment, an apparatus includes at least one memory configured to store an image of light transmitted through a material. The apparatus also includes at least one processor configured to analyze multiple regions of the image and determine one or more haze measurements associated with the material based on analyzing the multiple regions.

In a third embodiment, a system includes an image detector configured to capture an image of light transmitted through a material. The system also includes an analyzer configured to analyze multiple regions of the image and determine one or more haze measurements associated with the material based on analyzing the multiple regions.

DETAILED DESCRIPTION

FIGS. 1 through 3illustrate example systems for measuring haze of sheet materials or other materials according to this disclosure. As shown inFIG. 1, a system100is used to measure the haze of a material102. The material102here represents a moving web or sheet of non-opaque material, such as plastic. However, the material102could represent any other material(s) in any suitable form(s), such as glass.

In this example, the system100includes a light source104and optics106that are used to produce a collimated beam108. The light source104represents any suitable source of illumination. For example, the light source104could include one or more monochrome or narrow-band sources, such as one or more light emitting diodes (LEDs) or lasers. The light source104could also include one or more polychrome sources or multiple narrow-band sources, such as multiple LEDs or lasers. The light source104could further include spectrally rich sources, such as xenon or other gas-discharge sources, incandescent sources, black body sources, or wide-band LEDs. The light source104could optionally include filters or other components for spectral shaping, and the light source104could have continuous or pulsed operation.

The optics106create the collimated beam108using the illumination provided by the light source104. Any suitable optics106could be used, such as masks, lenses, mirrors, or prisms. The collimated beam108represents any suitable collimated beam of light. The collimated beam108could, for example, represent a beam of light with a circular cross-section having a diameter of at least 1 mm. The collimated beam108may have a radially symmetric intensity distribution and a small divergence angle (such as less than 1°). The collimated beam108may strike the material102at any suitable angle, such as 90°.

A light trap110helps to ensure that ambient light is substantially excluded from the measurement location of the material102. The light trap110could represent, for example, a suitable arrangement of baffles or annular light traps that exclude ambient light while providing an unhindered path for the collimated beam108. A housing112can support the components used to produce the collimated beam108and can also block ambient light.

Light from the collimated beam108strikes the material102and is transmitted through the material102, emerging as transmitted light. The transmitted light includes light114traveling along the same general path as the collimated beam108, meaning this light was not substantially scattered by the material102. The transmitted light also includes light116traveling along a canonical path that diverges away from the path of the collimated beam108, meaning this light was scattered by the material102to a more significant degree. The canonical path could have a subtending angle of at least 10° at its apex, and the canonical path could intersect the material102over a larger area than the collimated beam108. Note that the amount of light114and the amount of light116vary depending on the haze of the material102.

The light114and116strikes an image detector118, which captures an image of the light114and116. The image detector118could, for example, measure the intensity of the light directly incident on each pixel of the detector118. The image detector118could include pixels directly in line with the collimated beam108to measure the light114and additional pixels to measure the light116. The image detector118may include an imaging area that is large enough to capture most or all of the light116within the canonical path.

The image detector118includes any suitable image capturing device or devices, such as a charge-coupled device (CCD), a complimentary metal oxide semiconductor (CMOS) device, or a charge injection device (CID). In particular embodiments, the image detector118includes a two-dimensional detector array, such as an array of monochrome or RGB detectors. Also, the image detector118could have sufficient dynamic range so that pixels are not saturated during image measurements (even if all light from the collimated beam108strikes the pixels measuring the light114). Other components could also be used with the image detector118, such as an arbitrary spectral filter. Note that the light striking the image detector118could be unfocussed, although standard detector micro-optics or other non-focusing optics could be used. Also note that when a pulsed light source104is used, the image detector118can be synchronized with the light source104to capture images at the appropriate times.

A light trap120and a housing122help to ensure that ambient light is substantially excluded from the measurement location of the material102. The light trap120could exclude ambient light while providing an unhindered path for the light114and116to the detector118. The housing122could also support the components within the housing.

An analyzer124receives images captured by the image detector118and analyzes the images to determine one or more haze measurements for the material102. As described in more detail below, the analyzer124could process a captured image by identifying an amount of light striking different regions of the image detector118. For example, the analyzer124could measure the amount of light in a central disc of the image and in one or more concentric regions around the disc. These amounts of light can be used to calculate values such as raw haze, haze blur, and haze fuzz of the material102. The analyzer124includes any hardware, software, firmware, or combination thereof for analyzing images to determine haze measurements. The analyzer124could, for example, include one or more processors126and one or more memories128storing instructions and data used, generated, or collected by the processors126(such as images captured by the image detector118). The analyzer124could also include one or more network interfaces130facilitating communication over one or more networks, such as an Ethernet interface.

Haze measurements from the analyzer124could be used in any suitable manner. For example, the haze measurements could be provided to a controller132in a manufacturing system that produces the material102. The controller132could then adjust the production of the material102based on the measurements. In this way, the haze measurements provided by the analyzer124can be used to adjust pigments or process conditions (like temperature or pressure) used to produce the material102. This may help to ensure that the haze of the material102stays within defined limits. The haze measurements could also be provided to any other suitable destination132, such as to a database or other memory for storage or to a display for graphical presentation to a user. The haze measurements could be used for any other suitable purpose, such as to inspect the material102after manufacture. Note that the analyzer124could represent a stand-alone component or could be incorporated into a component or system that uses the haze measurements, such as when the analyzer124is implemented within the controller132.

As shown inFIG. 2, a system200is used to measure the haze of a material202, such as a sheet. The system200includes a light source204and optics206that produce a collimated beam208. The system200also includes a light trap210and a housing212. Light from the collimated beam208emerges from the material202as light214and light216. The system200further includes an image detector218, a light trap220, a housing222, and an analyzer224. These elements could be the same as or similar to the corresponding elements inFIG. 1. Although not shown, the analyzer224could be coupled to a controller or other external destination(s)132.

In this example, the light214and216emerging from the material202is not provided directly to the image detector218. Rather, the light214and216illuminates one side of a target surface226, and the image detector218captures an image of the other side of the target surface226. The target surface226can be optically thin so that the illumination by the light214and216on one side is minimally blurred or distorted when viewed from the other side. The target surface226may represent a flat surface that is generally parallel to the material202. The target surface226could be formed from any suitable material(s), such as one or more high diffuse translucent materials.

As shown inFIG. 3, a system300is used to measure the haze of a material302. The system300includes a light source304and optics306producing a collimated beam308. The system300also includes a light trap310and a housing312. Light from the collimated beam308emerges from the material302as light314and light316. The system300further includes an image detector318, a light trap320, a housing322, and an analyzer324. These elements could be the same as or similar to the corresponding elements inFIGS. 1 and 2. Also, the analyzer324could be coupled to a controller or other external destination(s)132.

In this example, the light314and316emerging from the material302is not provided directly to the image detector318. Rather, the light314and316is reflected off a target surface326to the image detector318. The target surface326may represent a generally flat surface that is parallel or at a slight or moderate angle to the material302. The target surface326reflects the light314and316to the image detector318, allowing the image detector318to be placed in a location that does not obstruct the light314and316. The target surface326could be formed from any suitable material(s), such as one or more highly reflective materials.

AlthoughFIGS. 1 through 3illustrate example systems100-300for measuring haze of sheet materials or other materials, various changes may be made toFIGS. 1 through 3. For example, any suitable number of light sources, optics, and collimated beams could be used to illuminate a material. Also, any suitable number of target surfaces, image detectors, and analyzers could be used to measure and analyze light from the material. Further, the arrangements and positions of the components in these figures are for illustration only. In addition, each system could include any other or additional components according to particular needs, such as mirrors, prisms, or other optics for folding a light path as needed.

FIG. 4illustrates an example image400used for measuring haze of sheet materials or other materials according to this disclosure. The image400shown inFIG. 4could, for example, be captured by any of the image detectors in the systems ofFIGS. 1 through 3.

In this example, the image400can be divided into multiple regions402-406. The region402represents a central disc or other area capturing light that has essentially passed directly through a material being examined. This light has therefore not been substantially scattered due to haze of the material. The regions404-406represent annual or other areas around the central region402. These regions404-406capture light that has been scattered to differing degrees due to haze of the material. The image400may also include one or more excluded regions408, where light in the excluded regions408is not analyzed.

Note that while the regions402-406are shown as being contiguous, there can optionally be annular or other spaces between these regions402-406. Also note that while the regions404-406are shown as being annular, each of these regions could be replaced by a disc or other shape that includes more-inner regions. For example, the region404could be replaced by a disc that covers both the regions402-404inFIG. 4, and the region406could be replaced by a disc that covers all three regions402-406inFIG. 4. Further note that the sizes, shapes, and positions of the regions402-406may be static or dynamic. For instance, the regions402-406can be dynamically centered around the centroid of the image400, the maximum of the image400, or the maximum of a smoothed version of the image400. Also, the diameters of the regions402-406could be provided by an external source or calculated based on a radial falloff curve of the pixel values (which can be determined using various heuristics). Other or additional techniques could also be used to define the regions402-406.

In some embodiments, to process the image400, an analyzer can add the pixel values in each region402-406to produce a sum for that region. Pixels that straddle a boundary between two regions could be handled in various ways. For example, those pixels could be omitted from the analysis. As another example, each pixel could be included in the region where the pixel's center is located. As a third example, a pixel can be fractionally included in both regions based on the percentage of the pixel in each region. As a fourth example, weighting factors can be applied to the pixels in a region before summing them. Weighting factors can be used, for instance, to reduce the effect of pixels that are near the boundaries of a region or that are in more than one region. Weighting factors can also be used to increase the effect of pixels that are not close to a region boundary or that are in only one region.

The sums associated with the regions402-406can then be used to calculate one or more haze measurements. For example, raw haze represents the amount of diffused light in at least one non-central region divided by the total amount of light. One example raw haze value can be calculated as:

Other haze measurements could include haze blur and haze fuzz. Haze blur represents a ratio of slightly diffused light to essentially direct light, which can be expressed as:

Haze⁢⁢Blur=Sum⁡(R2)Sum⁡(R1).(2)
Haze fuzz represents a ratio of moderately diffused light to slightly diffused light, which can be expressed as:

Haze⁢⁢Fuzz=Sum⁡(R3)Sum⁡(R2).(3)
Any other or additional haze measurements could be used here, such as other measurements based on ratios involving single regions or combinations of regions in the image400. Calibration curves could also be used to produce corrected haze blur and haze fuzz measurements.

AlthoughFIG. 4illustrates an example image400used for measuring haze of sheet materials or other materials, various changes may be made toFIG. 4. For example, the image400could include any suitable number of regions, and those regions could have any suitable size, shape, and position. Also, the image400could be analyzed in any other suitable manner.

FIGS. 5 through 8illustrate example variations for measuring haze of sheet materials or other materials according to this disclosure. As shown inFIG. 5, a single light beam502could be divided into multiple collimated beams504using optics506. The optics506could, for example, represent a beam splitter and a collimator. The beam splitter could include diffractive optics, prisms, mirrors, or other components. Each of the collimated beams504could be incident on a different area of the material being examined, such as by forming a linear or grid pattern or other spatial pattern. The collimated beams504may or may not have the same characteristics, such as diameter or intensity.

As shown inFIG. 6, multiple light beams602could be collimated to produce multiple collimated beams604using optics606. The light beams602could include monochrome or polychrome beams. The optics606could, for example, represent a collimator and may optionally include a beam splitter. Again, each of the collimated beams604could be incident on a different area of the material being examined. Also, the collimated beams604may or may not have the same characteristics, such as spectrum or polarization.

In either case, the analysis of the material may be performed using images of multiple areas of the material (where the multiple light beams504or604are transmitted through the material).FIG. 7illustrates an example image700used for measuring haze of sheet materials or other materials. Here, the image700includes multiple sets702of regions. The regions in each set702are similar to those shown inFIG. 4, but there are now four sets702of those regions. Haze measurements can be determined for each set702of regions. Note that each set702can be associated with its own beam(s) of light and that one or multiple image detectors could be used to capture images of the sets702. If a single detector is used, the image700can be segmented into different sections (each containing one set702), where the segmentation can be static or dynamic.

When used with the technique inFIG. 5, the analysis of the image700may identify spatial variations of the haze in the material. When used with the technique inFIG. 6, the analysis of the image700may identify variations of the haze based on changes in beam properties (such as wavelength or polarization).

FIG. 8illustrates another example system800for measuring haze of sheet materials or other materials. In this example, a material is illuminated using multiple collimated beams802. Light804associated with a first (monochrome) collimated beam is provided to an unfocussed monochrome image detector806. Light808associated with a second (polychrome) collimated beam is reflected off a mirror810and provided to an unfocussed polychrome image detector812. Light814-816associated with third and fourth (monochrome) collimated beams is provided to a translucent target surface818, and an image detector with focused optics820captures an image on the target surface818. Light822associated with a fifth (polychrome) collimated beam is divided by a dichroic mirror824, which provides part of the light822to an unfocussed image detector826. The other part of the light822is reflected off a mirror828and provided to another unfocussed image detector830.

As can be seen inFIGS. 5 through 8, a wide variety of techniques can be used to illuminate a material, direct light to or from the material, and measure light from the material. In general, light transmitted through a material can be detected by one or multiple image detectors and may optionally be split. Splitting using mirrors or prisms can be done so that each of multiple image detectors receives light from a different portion of the material. Splitting using gratings, dichroic mirrors, or filters can be done so that each of multiple image detectors receives light having different spectral characteristics. Each image detector can receive light from one or more illuminated areas of a material (such as the full canonical light from each illuminated area), and the image detectors may or may not be similar. The image detectors could differ in image scale, number of pixels, spectral sensitivity (whether monochrome or polychrome), and focusing optics (or lack thereof). In addition, polychrome light can be imaged in various ways, such as by integrating the light using a monochrome detector (optionally with bandpass or bandstop filters). The polychrome light can also be divided among multiple detectors receiving light in different spectral ranges (via filters or gratings). Spectral filters could be incorporated directly into photosensitive elements of an image detector, such as when a Bayer mask is used on a CCD or CMOS array.

AlthoughFIGS. 5 through 8illustrate example variations for measuring haze of sheet materials or other materials, various changes may be made toFIGS. 5 through 8. For example, any individual or subset of these variations could be used in any given situation. Also, a wide variety of other variations could also be made.

FIG. 9illustrates an example method900for measuring haze of sheet materials or other materials according to this disclosure. As shown inFIG. 9, a material is illuminated at step902. This could include, for example, illuminating a sheet of material using one or more collimated beams of light. An image of light that has interacted with the material is captured at step904. This could include, for example, capturing a monochrome or polychrome image of the light that has been transmitted through the sheet of material. The light can be received directly or indirectly from the material.

Multiple regions are identified in the captured image at step906. This could include, for example, identifying static or dynamic regions in the image. The regions could include a central disc as well as outer annual regions (or larger discs). The regions in the image are analyzed at step908. This could include, for example, summing the values of the pixels in each region to determine a total sum for that region. Pixels spanning multiple regions could be handled in any suitable manner.

One or more haze values are identified and used at step910. This could include, for example, using the sums associated with the different regions to calculate raw haze, haze blur, and haze fuzz values. This may also include using one or more calibration curves to adjust the computed haze values. The haze values could then be stored, output to a process controller or other destination, used to modify or control a production process, or used in any other suitable manner.

AlthoughFIG. 9illustrates an example method900for measuring haze of sheet materials or other materials, various changes may be made toFIG. 9. For example, as noted above, a number of variations could be used for illuminating a material, measuring light from the material, and analyzing the results. Also, while shown as a series of steps, various steps inFIG. 9could overlap, occur in parallel, or occur multiple times.