Patent Description:
Honeycomb bodies are used in a variety of applications, such as the construction of particulate filters and catalytic converters that treat unwanted components in a working fluid, such as pollutants in a combustion exhaust. The manufacture of honeycomb bodies may include inspection of the features of the bodies' honeycomb structures.

<CIT> discloses a method showing the features of the preamble of claim <NUM>.

Various approaches are described herein for, among other things, providing improved inspection of a honeycomb body or honeycomb extrusion die. Methods are described in which measurement data derived from multiple images of portions of a honeycomb body are first converted into a common reference frame and then combined rather than creating a composite image of the entire honeycomb body and taking measurements from the composite image. Additionally, an improved apparatus for imaging a honeycomb body is described and can be configured to reduce a pattern bias in images of the honeycomb body.

The invention provides a method of measuring features of a workpiece according to claim <NUM>. The method comprises capturing a first image of a first portion of the workpiece using a camera of an imaging system; determining, from the first image, a first plurality of measurements of the first portion of the workpiece in a first frame of reference of the first image; moving at least one of the workpiece or the camera relative to the other; capturing a second image of a second portion of the workpiece using the camera, wherein the first portion and the second portion at least partially overlap and share a common feature; determining, from the second image, a second plurality of measurements of the second portion of the workpiece in a second frame of reference of the second image; identifying the common feature in the first image and in the second image, wherein the common feature has a first location in the first frame of reference and a second location in the second frame of reference; determining a spatial relationship between the first frame of reference and the second frame of reference based on a comparison of the first location to the second location; converting the first plurality of measurements, the second plurality of measurements, or both, to a common frame of reference based at least in part on the spatial relationship; and creating a set of dimensions of features of the workpiece by combining the first and second pluralities of measurements as converted to the common frame of reference.

In some comparative examples, the moving comprises moving at least one of the workpiece or the camera a predefined distance and the spatial relationship between the first frame of reference and the second frame of reference is based at least in part on the predefined distance.

In some comparative examples, the method further comprises determining an error in moving at least one of the workpiece or the camera relative to each other.

In some comparative examples, the error is determined by comparing the predefined distance to a difference between the first and second locations in the common frame of reference. In some embodiments, the spatial relationship between the first frame of reference and the second frame of reference is based on the predefined distance and the error.

In some comparative examples, the common frame of reference is the first frame of reference. In some comparative examples, the common frame of reference is the second frame of reference.

In some comparative examples, the common frame of reference is a third frame of reference that is different from the first frame of reference and the second frame of reference.

In some comparative examples, the first and second frames of reference are both oriented with respect to a Cartesian coordinate system.

In some comparative examples, the method further comprises removing duplicate measurements after combining the first plurality of measurements and the second plurality of measurements in the common frame of reference.

In some comparative examples, the common feature comprises a dimension defined between two points.

In some comparative examples, the workpiece is a honeycomb body defining a plurality of longitudinal cells. In some comparative examples, the common feature is a centroid of a longitudinal cell of the honeycomb body.

In some comparative examples, the workpiece comprises a honeycomb body and the common feature comprises a length of a wall of a longitudinal cell of the honeycomb body.

In some comparative examples, the dimension comprises a distance between a first centroid of a first cell of the honeycomb body and a second centroid of a second cell of the honeycomb body.

In some comparative examples, the imaging system comprises the camera, a lens, a first light source, and a second light source.

In some comparative examples, the first light source is configured to provide bright field lighting, and wherein the second light source is configured to provide dark field lighting.

In some comparative examples, the lens defines an optical axis, the first light source defines a first illumination axis, and the second light source defines a second illumination axis, wherein the first illumination axis is angled relative to the optical axis by an angle α that is in a range between <NUM>° and <NUM>°, and the second illumination axis is angled relative to the optical axis by an angle θ that is in a range between <NUM>° and <NUM>°.

In some comparative examples, the first light source is a ring light and the second light source is a ring light.

In some comparative examples, the workpiece is illuminated by the first light source and the second light source simultaneously while capturing the first and second images.

In some comparative examples, the workpiece is stationary relative to the camera of the imaging system while capturing the first and second images.

In some comparative examples, the method further comprises capturing a third image of a third portion of the workpiece, wherein the common feature is a first common feature and the third portion overlaps with and comprises a second common feature with the second image; determining, from the third image, a third plurality of measurements of the third portion of the workpiece in a third frame of reference of the third image; identifying the second common feature in the second image and in the third image, wherein the second common feature has a third location in the second frame of reference and a fourth location in the third frame of reference; comparing the third location to the fourth location and defining a second spatial relationship between the second frame of reference and the third frame of reference based on the comparing;.

converting the third plurality of measurements to the common frame of reference based at least in part on the second spatial relationship; and combining the third plurality of measurements, as converted to the common frame of reference, into the set of dimensions.

The invention provides a method of measuring features of a workpiece according to claim <NUM>. The method comprises providing an imaging system; capturing an image of a first portion of the workpiece, wherein the image of the first portion of the workpiece defines a frame of reference; calculating a first plurality of measurements based at least in part on the image of the first portion of the workpiece; capturing an image of a second portion of the workpiece, wherein the first portion of the workpiece and the second portion of the workpiece comprise a plurality of common features, wherein the second portion comprises at least one feature that is not included in the first portion of the workpiece; calculating a second plurality of measurements based at least in part on the image of the second portion of the workpiece, wherein at least one of the first plurality of measurements is a first reference dimension defined by the common features, wherein at least one of the second plurality of measurements is a second reference dimension defined by the common features, wherein the first reference dimension is defined by a dimension between the common features based at least in part on the image of the first portion of the workpiece and the second reference dimension is defined by the same dimension between the common features based at least in part on the image of the second portion of the workpiece; comparing the first reference dimension to the second reference dimension to calculate a transformation;.

applying the transformation to the second plurality of measurements to convert the second plurality of measurements into the frame of reference; and combining the first plurality of measurements and the converted second plurality of measurements.

In another aspect, not covered by the scope of the claims, an imaging system for measuring dimensions of a workpiece is provided. The system comprises a camera configured to capture images of the workpiece; an actuator configured to move the camera relative to the workpiece or the workpiece relative to the camera; a controller in data communication with the camera and the actuator and configured to cause the imaging system to: capture a first image of a first portion of the workpiece with the camera; determine a first plurality of measurements of features of the workpiece from the first image, wherein the first plurality of measurements is defined with respect to a first frame of reference of the first image; position a field of view of the camera with respect to a second portion of the workpiece with the actuator, wherein the second portion overlaps with the first portion and comprises a common feature with the first portion; capture a second image of the second portion of the workpiece; determine a second plurality of measurements of features of the workpiece from the second image, wherein the second plurality of measurements is defined with respect to a second frame of reference of the second image; identify a first location of the common feature in the first image and a second location of the common feature in the second image; determine a spatial relationship between the first frame of reference and the second frame of reference based on a comparison of the first location to the second location; convert the first plurality of measurements, the second plurality of measurements, or both, to a common reference frame based on the spatial relationship; and create a set of dimensions of features of the workpiece by combining together the first and second pluralities of measurements as converted into the common reference frame.

In some examples, the actuator is configured to position the camera by moving at least one of the workpiece or the camera a predefined distance and the spatial relationship between the first frame of reference and the second frame of reference is based at least in part on the predefined distance.

In some examples, the controller is further configured to determine an error in movement of at least one of the workpiece or the camera relative to each other when positioning the field of view of the camera with respect to the second portion of the workpiece.

In some examples, the error is determined by comparing the predefined distance to a difference between the first and second locations in the common frame of reference.

In some examples, the spatial relationship between the first frame of reference and the second frame of reference is based on the predefined distance and the error.

In some examples, the common frame of reference is the first frame of reference or the second frame of reference.

In some examples, the common frame of reference is a third frame of reference that is different from the first frame of reference and the second frame of reference.

In some examples, the workpiece is a honeycomb body defining a plurality of longitudinal cells.

In some examples, the common feature is a centroid of a longitudinal cell of the honeycomb body.

Further embodiments are described below in the Detailed Description.

The accompanying drawings, which are incorporated herein and form part of the specification, illustrate embodiments of the present invention and, together with the description, further serve to explain the principles involved and to enable a person skilled in the relevant art(s) to make and use the disclosed technologies.

The features and advantages of the disclosed technologies will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout.

The following detailed description refers to the accompanying drawings. However, the scope of the present invention is defined by the appended claims. Thus, embodiments beyond those shown in the accompanying drawings, such as modified versions of the illustrated embodiments, may nevertheless be encompassed by the present invention.

References in the specification to "one embodiment," "an embodiment," "an example embodiment," or the like, indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Furthermore, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the relevant art(s) to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Example embodiments described herein provide improvements over known methods and systems for measuring features of honeycomb bodies. Example embodiments of the method of measuring features of a workpiece comprise capturing an image of a first portion of the workpiece, determining a first plurality of measurements based on the image of the first portion, capturing an image of a second portion of the workpiece, determining a second plurality of measurements based on the image of the second portion, locating a common feature in an overlapping region between each of the images, using the locations of the common feature in the images to convert the first plurality of measurements, the second plurality of measurements, or both, to a common frame of reference, and combining the measurements in the common frame of reference.

The improvements provide numerous advantages over known systems such as those utilizing flatbed scanner and microscope-based imaging systems. The improvements include combining measurement data together, instead of stitching together an image composite image, which reduces errors in measurement data that can arise when measurements are determined on a composite image formed by joining images together. In an example embodiment, the reduced error in the measurement data can be used to more accurately predict performance characteristics of the workpiece, such as isostatic strength. The improvements also reduce pattern bias in the images while reducing the time to capture images across an end face of a workpiece (e.g., honeycomb body or honeycomb extrusion die). In some instances, the improvements also provide higher resolution images of portions of a workpiece. Still further, the improvements are effective for workpieces that are constructed from dark and light materials and allow inspection of an entire end face of a workpiece in a shorter period of time.

<FIG> illustrate an exemplary honeycomb body <NUM>. The honeycomb body <NUM> comprises a plurality of spaced and intersecting inner walls <NUM>, or webs, extending longitudinally through the honeycomb body <NUM> from a first end face <NUM> to a second end face <NUM>. The inner walls <NUM> combine to define a plurality of channels <NUM>, or cells, that form a cellular honeycomb structure of the honeycomb body <NUM>. The honeycomb body <NUM> can also comprise peripheral channels <NUM> that are generally partial channels that intersect an outer skin <NUM> of the honeycomb body <NUM>. As illustrated, the honeycomb body <NUM> comprises channels <NUM> having a square cross-sectional shape, but the channels <NUM> can have other cross-sectional shapes, such as triangular, hexagonal, octagonal, wedged, or combinations of these or other shapes. Similarly, as illustrated, the honeycomb body <NUM> has a circular cross-sectional shape, but other shapes can be utilized, such as rectangular, square, triangular or tri-lobed, or ellipsoidal, among others. The honeycomb body <NUM> defines a longitudinal axis L that extends between the first end face <NUM> and the second end face <NUM> and that is substantially parallel to a longitudinal axis of the channels <NUM>.

The honeycomb body <NUM> can be formed in any desired manner, e.g., by extruding a ceramic-forming mixture through an extrusion die to form a green body, drying the green body, cutting the green body to length, and firing the green body to form a ceramic material. The ceramic material of the honeycomb body <NUM> can be a porous ceramic material. The honeycomb body can be inspected when green (before firing) or ceramic (after firing). The honeycomb body <NUM> can be utilized in a catalytic converter assembly by loading the walls <NUM> with a catalytic material and/or utilized in a particulate filter assembly by plugging some of the channels <NUM> (e.g., plugging the channels <NUM> alternatingly at the inlet and outlet faces).

Referring to <FIG>, an example imaging system <NUM> that can be used to capture high-resolution images of the honeycomb body <NUM> will be described. The imaging system <NUM> can be used to capture images of portions of the honeycomb body <NUM> that can be analyzed using machine vision software to collect measurement data for features of the honeycomb body <NUM>. In some embodiments, the imaging system <NUM> is configured to collect images of the honeycomb body <NUM> having resolution that is at least <NUM> x <NUM> pixels, at least <NUM>,<NUM> x <NUM>,<NUM> pixels, or even at least <NUM>,<NUM> x <NUM>,<NUM> pixels. The imaging apparatus <NUM> comprises a camera <NUM> and a lens <NUM>. As discussed herein, the imaging apparatus <NUM> can also comprise a first light source <NUM>, a second light source <NUM>, a part holder <NUM>, and a controller <NUM>.

The camera <NUM> is disposed on a first side of the honeycomb body <NUM> and is configured to capture high-resolution images of an end face of the honeycomb body <NUM> (e.g., the inlet face <NUM> or the outlet face <NUM>). The camera <NUM> can be a digital camera that is configured to record digital image data corresponding to the honeycomb body <NUM> so that measurement data of features of the honeycomb body <NUM> can be collected. The digital image data is based at least in part on an image of the honeycomb body <NUM> that passes through the lens <NUM> and is projected onto a digital image sensor in the camera <NUM>. The camera <NUM> can be configured to collect monochromatic or multi-color image data. Exemplary digital cameras that can be employed are the Dalsa Falcon <NUM>, <NUM> MP digital camera; the Prosilica GT <NUM>, <NUM> MP digital camera; and the Adimec S25A80, <NUM> MP digital camera, although other cameras are possible. In some embodiments, the camera <NUM> has a resolution relating to a physical dimension of the honeycomb body <NUM> that corresponds to approximately <NUM>-<NUM> per pixel, such as µm per pixel.

The lens <NUM> has an optical axis OP. The lens <NUM> can be integral to the camera <NUM> or otherwise optically coupled to the camera <NUM> so that an image of the honeycomb body <NUM> (e.g., in the form of light reflected from the honeycomb body <NUM>) is passed through the lens <NUM> and directed to the camera <NUM>, e.g., to image sensors of the camera <NUM>. The lens <NUM> can provide any selected magnification to provide the desired dimensional resolution. The lens can be constructed as a telecentric or macro lens. In an example embodiment, the lens is a telecentric lens having 1x magnification, telecentricity of <NUM>°, and distortion of <NUM>%. Example lenses that may be employed include the TC16M036 lens offered by Opto Engineering of Houston, TX.

The imaging system can comprise a movable stage <NUM>. The movable stage <NUM> can be configured to provide relative movement between the honeycomb body <NUM> and the camera <NUM>, such as to move the camera <NUM> and lens <NUM> in a direction toward and away from the honeycomb body <NUM>, such as in a direction parallel to the Z-axis illustrated in <FIG>. The movable stage <NUM> can be used to provide relative movement so that a selected portion of the honeycomb body <NUM> is disposed within the depth of field of the lens <NUM>. In an example embodiment, the depth of field of the lens <NUM> is less than <NUM>, and in another example embodiment the depth of field of the lens <NUM> is about <NUM>.

The first light source <NUM> can be disposed on the first side of the honeycomb body <NUM>, i.e., the same side of the honeycomb body <NUM> as the camera <NUM> and the lens <NUM>. That location enables the first light source <NUM> to directly illuminate the end face of the honeycomb body <NUM> closest to the lens <NUM>. The first light source <NUM> can be disposed adjacent the lens <NUM> and can be coupled to the lens <NUM>. The first light source <NUM> can be a high intensity monochromatic ring light that is generally annular and that circumscribes the optical axis OP (and the field of view) of the lens <NUM>. The first light source <NUM> can be constructed from a plurality of light sources, such as light-emitting diodes (LED) distributed around the optical axis. In some embodiments, the light sources of the first light source <NUM> are selected to emit uniform monochromatic light of a selected color, such as monochromatic green light.

As shown in <FIG>, the first light source <NUM> can be configured to provide direct, bright field illumination of the honeycomb body <NUM>. In some embodiments, the first light source <NUM> provides bright field illumination in which an illumination axis forms a low illumination angle α with the optical axis OP of the lens <NUM>, such as in a range between about <NUM>° (parallel) and about <NUM>°, or between about <NUM>° and <NUM>°. The low illumination angle α results in light reflecting off the end face of the honeycomb body <NUM> being directed back into the lens <NUM>. In an example embodiment, the first light source <NUM> is constructed as a ring light, and in some embodiments the first light source <NUM> is coupled to the lens <NUM>. In an example embodiment, the illumination angle α provided by light source <NUM> is less than <NUM>° relative to the optical axis OP of the lens <NUM>, in another example embodiment the illumination angle α is less than <NUM>°, and in another example embodiment the illumination angle α is between about <NUM>° and about <NUM>°.

The imaging system <NUM> can optionally include a second light source <NUM> configured to provide dark field illumination of the honeycomb body <NUM>. It was determined by the inventors that the addition of a light source providing dark field illumination could be useful in reducing a pattern bias, i.e., distortion of portions of an image of the end face of the honeycomb body <NUM>, which was included in some images taken only with bright illumination. In some embodiments, the second light source <NUM> provides an illumination axis that forms a high illumination angle θ with the optical axis OP of the lens <NUM>, such as in a range between about <NUM>° and about <NUM>°, or about <NUM>° and about <NUM>°. In some embodiments, the second light source <NUM> is constructed as a ring light similar to the construction of the first light source <NUM> but providing a different illumination angle. In an example embodiment, the illumination angle θ provided by the second light source <NUM> is greater than <NUM>° or even greater than <NUM>° relative to the optical axis OP of the lens <NUM>, greater than <NUM>°, or between about <NUM>° and about <NUM>°.

The second light source <NUM> can be located close to the honeycomb body <NUM> to provide dark field illumination. The second light source <NUM> can be disposed as close to the honeycomb body <NUM> as possible without risking impact between the honeycomb body <NUM> and the second light source <NUM> during relative movement between the honeycomb body <NUM> and the imaging system <NUM>. In an example embodiment, the second light source <NUM> is spaced from the honeycomb body <NUM> by less than <NUM>, and in another example embodiment by about <NUM>-<NUM>.

The part holder <NUM> is configured to hold and/or position the honeycomb body <NUM> in a desired orientation so that selected portions of the honeycomb body <NUM> can be imaged. The part holder <NUM> comprises a movable stage <NUM>, such as an XY stage and/or a tilt stage so that the honeycomb body <NUM> can be moved relative to the camera <NUM> and lens <NUM>. The relative X-axis, Y-axis, and Z-axis motion between the honeycomb body <NUM> and the camera <NUM> and lens <NUM> can be accomplished using actuators that are coupled directly to the part holder <NUM>, directly to the camera <NUM> and lens <NUM>, or both.

The controller <NUM> can control the relative movement between the honeycomb body <NUM> and the imaging system <NUM>, the capturing of images, the processing of the images, and the combining together of the measurement data as described herein. The controller <NUM> can comprise a processor, data storage, and a display. Together with the hardware components, the controller <NUM> can include software configured to instruct operation of the components of the imaging system <NUM>, such as for the camera <NUM> to capture images or for the part holder <NUM> to alter the relative positions of the honeycomb body <NUM> and the imaging system <NUM>. Additionally, the controller <NUM> can be configured to perform feature measurement by executing image measurement software. The controller <NUM> can also include image acquisition and processing software that provides a user interface for collecting and processing images.

In some embodiments, the imaging system <NUM> includes a distance sensor <NUM>. The distance sensor <NUM> can be used to identify the presence or absence of the honeycomb body <NUM> and/or the location of the honeycomb body <NUM>, such as by measuring the distance between the honeycomb body <NUM> and the lens <NUM>. The distance between the honeycomb body <NUM> and the lens <NUM> can be used to control the movable stage <NUM> for the camera <NUM> and the lens <NUM>, and the movable stage <NUM> for the honeycomb body <NUM> so that the honeycomb body <NUM> is positioned in the depth of field of the lens <NUM> for imaging. In some embodiments, the distance sensor <NUM> is a laser line profilometer.

Various physical features of the honeycomb body <NUM> can be measured using the imaging system <NUM>. For example, dimensions of the walls <NUM> and/or of the channels <NUM> can be measured. In some instances, the features captured and measured using the imaging system <NUM> include physical imperfections, i.e., geometries (e.g., dimensions or shapes) of the honeycomb body <NUM> that are different than a designed geometry. For example, a wall having a break, crack, tear, or gap can be identified as an imperfection. Geometric imperfections may result during extrusion or other manufacturing processes of the honeycomb body <NUM> and those imperfections may alter characteristics of the honeycomb body <NUM>, such as isostatic strength.

Referring to <FIG>, a plurality of images are captured of the honeycomb body <NUM>, which relate to different portions of the honeycomb body <NUM>. The honeycomb body <NUM> and the imaging system <NUM> are moved relative to each other to image the different portions of the honeycomb body <NUM>, and the movement can be stepped or continuous. In an example embodiment, the images are captured by stepping across the honeycomb body <NUM> with the imaging system <NUM> following a two-dimensional grid pattern oriented over an end face of the honeycomb body <NUM>, such as the grid shown in <FIG>. The honeycomb body <NUM> and imaging system <NUM> can be held stationary relative to each other during the capturing of each image. Capturing images along the grid pattern results in the plurality of images being arranged in rows 444a-g and columns 446a-g of images. The grid can be sized based on a particular part size, such as a diameter of a selected honeycomb body. Alternatively, the grid can have a size large enough to encompass a maximum sized honeycomb body, which allows the grid to capture images of any workpiece having a size up to the maximum.

Collecting the plurality of images over the honeycomb body <NUM>, can result in the images having higher resolution than would otherwise be possible by the camera used to collect the images. That is, each image can be configured to capture a portion of the honeycomb body <NUM> instead of capturing the full honeycomb body. As a result, the full resolution of the camera can be dedicated to capturing only a portion of the honeycomb body <NUM> in each image.

As illustrated in <FIG>, the grid pattern can be truncated so that the plurality of images need not include the same number of images in each row or in each column. For example, images positioned in the grid pattern that do not capture any portion of the honeycomb body <NUM> need not be collected.

Each captured image at least partially overlaps one or more adjacent images. Adjacent images are positioned so that the portions of the honeycomb body <NUM> captured in the adjacent images include at least one common feature. For example, a common feature can be a centroid of a particular one of the channels <NUM>, a particular corner of a particular one of the channels <NUM>, or other visually identifiable feature. As described herein, the overlap of the adjacent images, and the common feature captured by the images, provides information used to combine together measurement data gathered from the plurality of images. As will be described in greater detail below, the identified locations of the common features in adjacent images are used to determine spatial relationships between the adjacent images that are in turn used to convert measurement data determined from the adjacent images into a common frame of reference. After the measurement data is converted to a common frame of reference, the data can be combined to create a set of dimensions of features of the honeycomb body <NUM> without requiring the images to be stitched together.

In the embodiment of <FIG>, the first row 444a of the images comprises five images. For ease of discussion herein, three such images are identified as a first image <NUM>, a second image <NUM>, and a third image <NUM>. The first image <NUM> can be captured from a first relative position between the honeycomb body <NUM> and the imaging system <NUM>. The second image <NUM> can be captured from a second relative position between the honeycomb body <NUM> and the imaging system <NUM>. The third image <NUM> can be captured from a third relative position between the honeycomb body <NUM> and the imaging system <NUM>, and so on for each successive image in each row and column. Adjacent images in the row include overlapping regions. For example, an overlapping region <NUM> is created between the first image <NUM> and the second image <NUM> by selecting a distance between the first relative position and the second position that is less than a width of the portion of the honeycomb body <NUM> depicted by the first image <NUM>. The overlapping region <NUM> assures that there are common features of the honeycomb body shown in the adjacent images, i.e., identical features are shown in both the first image <NUM> and in the second image <NUM>. Similarly, the second image <NUM> also overlaps with the third image <NUM> as shown by overlapping region <NUM>. Additionally, adjacent images arranged in each column can include an overlapping region. For example, portions of the first image <NUM> of the first row 444a and the second image <NUM> of the second row 444b, which are both included in column 446b, overlap at overlapping region <NUM>. In an example grid pattern, each image depicts a <NUM> to <NUM> square field of view, such as about a <NUM> to <NUM> square field of view, with a step size between images that is between about <NUM>% to <NUM>% of the width of the field of view. For example, in one embodiment, a step size of about <NUM> is utilized for an image size of about <NUM> to <NUM>, thereby creating about <NUM> to <NUM> of overlap between adjacent images.

The measurement data generated for each image can include image identifying measurements and cell attribute measurements. The image identifying measurements can include an image X index (i.e., an x-coordinate for a known location of the image, such as the x-coordinate of a centroid of the image) and/or an image Y index (i.e., an y-coordinate for a known location of the image, such as the y-coordinate of the centroid of the image). By use of the X and Y indexes, the relative position of the images with respect to each other can be established. For example, referring to the example of <FIG>, the X index can be correlated to the column, while the Y index can be correlated to the row in which each image is in. With knowledge of the relative positions, e.g., row and column, adjacency between the images can also be determined.

The cell attribute measurements can include cell wall angle, horizontal and vertical cell pitch, horizontal and vertical wall thickness, and horizontal and vertical wall bow, shear angles, web distortion, cell area and aspect ratio, perimeter length, etc. The measurement data can be extracted from the images using machine vision software executed by one or more processors (e.g., the processor included in controller <NUM>). An example of a system and method of extracting dimensional data from images is described in <CIT> and in <CIT>. The one or more processors can be incorporated into the imaging system or they can be separate processors communicating over a network. In an example, a computer vision library, such as OpenCV, can be employed.

Thus, as described above, measurement data can be gathered of various features (e.g., dimension data of the cells <NUM> and/or walls <NUM> of the honeycomb body <NUM>) captured in each of the various images. Advantageously, the system <NUM> enables the measurement data to be combined into a common data set even though portions of the measurement data is extracted from a plurality of different images. In particular, the system <NUM> enables the combination of such measurement data even if error is introduced during moving the camera or honeycomb body between capturing subsequent images. Furthermore, as described herein, the system <NUM> can create such a combined measurement data set without the need to stitch together all of the images into a single composite image. Advantageously, avoiding the need to stitch together images significantly reduces the computational time and resources necessary to extract measurement data from captured images while maintaining the images to be analyzed at a pixel resolution that is not otherwise feasible.

Referring to <FIG>, further details of operation of the imaging system <NUM> can be appreciated. As described above, the honeycomb body <NUM> is imaged by capturing a plurality of images, such as a first image <NUM> and a second image <NUM> (e.g., akin to images <NUM> and <NUM> described with respect to <FIG>). For clarity, the field of view of the first image <NUM> are indicated in a dash-dot line (-. -), while the field of view of the second image <NUM> are indicated in a dash-double dot line (-. -) The first and second images <NUM> and <NUM> are adjacently located, and share an overlapping region <NUM> (e.g., akin to the overlapping region <NUM> of <FIG>). The features, e.g., physical structures or geometries, in the portions of the honeycomb body <NUM> that is depicted in the overlapping region <NUM> are thus common to both first image <NUM> and second image <NUM> (and also in common to the respective first portion and second portion of the honeycomb body <NUM> that are depicted by first image <NUM> and second image <NUM>).

In the example of <FIG>, a centroid C1 of a first cell <NUM> is located in the overlapping region <NUM> and thus can be used as a common feature for both first image <NUM> and second image <NUM>. That is, both the first image <NUM> and the second image <NUM> depict the centroid C1 of the first cell <NUM>, so that the centroid C1 can be identified in each of the first image <NUM> and the second image <NUM>. By controlling and monitoring of the status of the movable stages <NUM> and <NUM>, the position of the honeycomb body <NUM> relative to the camera <NUM> (and/or lens <NUM>) when each of the first image <NUM> and the second image <NUM> is captured is known, e.g., with respect to a global reference frame, as indicated in <FIG>. The global reference can be utilized to determine the positioning of the images relative to each other, e.g., the X- and Y- indexes as discussed above. For example, referring also to the example of <FIG>, the global reference frame can be the frame in which the rows and columns are determined. Thus, the camera <NUM> and/or the honeycomb body <NUM> can be stepped in predetermined amounts relative to the other (i.e., the step size as described above) in the X-and/or Y- directions of the global reference frame to successively capture each image.

As described in more detail below, while the position of the camera <NUM> (and/or lens <NUM>) relative to the honeycomb body <NUM> is referred to above as "known", there may be some degree of uncertainty or error in the accuracy of this position. Accordingly, each captured image can have a frame of reference that is separate from the global frame of reference, e.g., the first image <NUM> has a first frame of reference and the second image <NUM> has a second frame of reference in <FIG>. The frames of reference can use the same coordinate system (e.g., X- and Y- axes) and orientation as the global reference frame (e.g., the X- and Y-axes of the first and second frames of reference of the first and second images <NUM> and <NUM> can be parallel respectively to the X- and Y- axes of the global frame of reference). For consistency, the frames of reference of the images can be set at the same location relative to each image, for example, in the bottom left of each image with respect to the orientation of <FIG>.

Accordingly, the centroid C1 is positioned at a first location, having first coordinates (X11, Y11) within the first frame of reference defined by the first image <NUM> as shown in <FIG>. As used herein a coordinate Xnm is used to denote an X-axis coordinate of a feature "n" in the "m" frame of reference. Thus, X11 indicates a first common feature (e.g., the centroid C1) in a first frame of reference, while X12 indicates the first common feature (e.g., the centroid C1) in a second frame of reference. Thus, after moving the camera <NUM> relative to the honeycomb body <NUM> to capture the second image <NUM>, the same centroid C1 is also positioned at a second location, having second coordinates (X12, Y12), within the second frame of reference defined by the second image <NUM>, as shown in <FIG>. For example, with respect to <FIG>, the first position is toward the right hand side with respect to the first frame of reference of first image <NUM>, while the second position is toward the far left hand side with respect to the second frame of reference of second image <NUM>. In other words, the value of the coordinate X11 is expected to be larger than the value of the coordinate X12, since these coordinates are determined with respect to their corresponding frames of reference, not with respect to the global frame of reference.

Referring to <FIG>, if the relative positioning of the honeycomb body <NUM> relative to the camera <NUM> (and/or lens <NUM>) presents no movement error between capturing the first and second images, then the field of view of the first image <NUM> is shifted relative to the field of view of the second image <NUM> by an expected distance S in the global reference frame. That is, the expected distance S represents the step size that the controller <NUM> instructs the movable stages <NUM> and/or <NUM> to undertake. Accordingly, if there is no error in movement, and if the size of the field of view is unchanged, then the second coordinates (X12, Y12) in the second frame of reference can be derived by subtracting the expected distance (e.g., distance S) from the first coordinates (X11, Y11) of centroid C1. In the illustrated example, the second image <NUM> is offset in only the X-direction relative to the first image <NUM> (i.e., the first image <NUM> and second image <NUM> are in the same row, and thus, the Y-index or coordinate in the global reference frame should be the same). Accordingly, measurements, e.g., the coordinates of the centroid C1, determined in one frame of reference can be converted (assuming no error) into the other frame of reference based at least in part on the distance S according to the following coordinate relationships:
If adjacency between first image and second image is in X-direction with step size S: <MAT> <MAT>.

If adjacency between first image and second image is in Y-direction with step size of S: <MAT> <MAT>.

Based on those relationships, the coordinates of every measured feature from either of the first image <NUM> and the second image <NUM> can be converted into either frame of reference. For example, coordinates measured in the first frame of reference, defined by the first image <NUM>, can be converted to coordinates in the second frame of reference, defined by the second image <NUM>, by subtracting the distance S to each X-coordinate, while the Y-coordinate remains unchanged. Thus, this conversation enables either the first frame of reference or the second frame of reference to be used as a common frame of reference. Measurements corresponding to other features of the honeycomb body <NUM> can also be converted into a common frame of reference in a similar way. For example, a centroid Cn of a cell "n" that is depicted in the second image has coordinates in the second frame of reference (Xn2, Yn2) that can be converted into coordinates in the first frame of reference. When each of the desired measurements has been converted to a common frame of reference, they can be combined into a single common measurement data set, without requiring a combination of the image data of the plurality of images.

Measurements of other features shown in the second image <NUM> can also be determined relative to the common feature in the second image <NUM>. In particular, measurements of features that are only shown in the second image <NUM> can be combined together with features only shown in other images by relating them to the common feature. For example, measurements such as coordinates of the centroid Cn that is only shown in the second image <NUM> can be determined. Within the second image <NUM>, the common feature, centroid C1, and the centroid Cn are spaced from each other in the X-direction by a distance dx and in the Y-direction by a distance dy, resulting in the coordinates having following relationships: <MAT> <MAT> When multiple measurements determined from multiple images are converted into a common frame of reference, the measurements can be combined together into a single common measurement data set.

Although the described example includes a second image <NUM> that is translated only in the X direction relative to the first image <NUM> by distance S, the images can be offset in either, or both, the X and Y directions and the coordinate relationships altered accordingly. For example, combining measurement data from a plurality of images in a grid pattern, such as that shown in <FIG>, requires applying different spatial relationships for each image relative to a common frame of reference.

Additional images can be captured and measurements collected from the image. Measurement data generated from subsequent images can be converted into the common frame of reference using the conversions from intervening adjacent images. For example, measurements generated from a third image that is spaced from the first image <NUM> so that they do not include any overlapping region, can be converted into a common frame of reference by combining the conversion of measurements between the first image <NUM> and the second image <NUM>, and the conversion of measurements between the second image <NUM> and the third image.

In another example, the measurements can be converted to a common frame of reference after determining and/or correcting for a positioning error. For example, the positioning error can be determined by comparing an expected location of a common feature in a given frame of reference to an actual location of the common feature in that frame of reference. For example, as described above, it is expected that X12 = X11 - S and Y12 = Y<NUM> in the example described above. However, the error between the expected location and the actual location can be introduced when moving the camera <NUM> and honeycomb body <NUM> relative to each other between the capture of each successive image. For example, the second location of the centroid C1 can be in a position within the second image <NUM> that is different than the expected second location, as shown by the dashed lines in <FIG>. In particular, the actual second location is illustrated as C1' and has coordinates (X<NUM>', Y12'), while the expected second location has coordinates (X12, Y12). In the illustrated example, the error in the relative positioning results in an X-coordinate error (ex1) and a Y-coordinate error (ey1), and the coordinates can be converted using the following relationships:
If adjacency between first image and second image is in X-direction with step size of S: <MAT> <MAT>.

Based on those relationships, the coordinates of every measured feature from the second image <NUM> can be more accurately converted from coordinates in the second frame of reference, defined by the second image <NUM>, to coordinates in the first frame of reference, defined by the first image <NUM>, by adjusting each X-coordinate by distance S and the error in the X-axis, while adjusting the Y-coordinates by the error in the Y-axis.

Referring to <FIG> a plurality of common features shown in an overlapping region can also be used to determine any scaling error (change in the size of the field of view of the lens <NUM> when capturing different images) before combining the measurement data. The first image <NUM> depicts a first portion of the honeycomb body <NUM> that includes a first feature, e.g., the centroid C1 of the first cell <NUM>, and a second feature, e.g., a centroid C2 of a second cell <NUM>. The second image <NUM> depicts a second portion of the honeycomb body <NUM> and includes at least a portion of the first portion of the honeycomb body <NUM> to define an overlapping region <NUM>. The first image <NUM> and the second image <NUM> are sized and oriented so that the overlapping region <NUM> includes the centroid C1 of the first cell <NUM> and the centroid C2 of the second cell <NUM>. As a result, both the first image <NUM> and the second image <NUM> depict the centroid C1 of the first cell <NUM> and the centroid C2 of the second cell <NUM>.

The centroids provide common features in the first image <NUM> and the second image <NUM>. A dimension, such as a distance between the centroids, that can be measured in the first image <NUM> and the second image <NUM> can be used to normalize the measurement data generated from the images to assure that the images depict the portions of the honeycomb body <NUM> at the same scale or magnification. For example, generating measurement data from the images can include generating a distance between centroid C1 and centroid C2 based on the first image <NUM> and a distance between centroid C1 and centroid C2 based on the second image <NUM>. The distance between centroid C1 and centroid C2 extracted from the first image <NUM> defines a first reference dimension R1, shown in <FIG>. The distance between centroid C1 and centroid C2 extracted from the second image <NUM> defines a second reference dimension R2, shown in <FIG>. The first reference dimension R1 is compared to the second reference dimension R2 to calculate a scaling error. Which can be applied to measurement data from the measurement data taken from the plurality of images to normalize all of the measurement data before it is combined into common measurement data set.

Next, combining the data comprises combining the measurement data into a single common measurement data set. For example, the measurement data extracted from the baseline image and the converted measurement data extracted from subsequent images are combined into a single set of measurement data for the entire honeycomb body <NUM>. The step of combining the measurement data can also include removing duplicative measurement data resulting from measurements extracted from overlapping regions of the images. As a result, a single set of measurement data is created that reduces errors caused by imaging and that is free of duplicative measurement data.

<FIG> depicts a flowchart <NUM> for measuring features of a workpiece, such as the honeycomb body <NUM>. Since honeycomb extrusion dies have features corresponding to the features of honeycomb body <NUM> (e.g., slots of the extrusion die forming the walls <NUM> and pins of the extrusion die forming the channels <NUM>), the imagining system <NUM> and method <NUM> can be utilized for inspecting the dimensions of the pins and slots of honeycomb extrusion dies, as both honeycomb bodies and honeycomb extrusion dies are workpieces having the herein described honeycomb patterns. For example, the image of <FIG> could also represent a honeycomb extrusion die with the reference numeral <NUM> identifying pins and the reference numeral <NUM> identifying slots formed between the pins. Flowchart <NUM> can be performed using the imaging system <NUM> shown in <FIG> and as described with respect to <FIG>, <FIG>, and <FIG>. Further structural and operational embodiments will be apparent to persons skilled in the relevant art(s) based on the discussion regarding the flowchart <NUM>.

As shown in <FIG>, the method of flowchart <NUM> begins at step <NUM>. In step <NUM>, inspection of a workpiece (e.g., the honeycomb body <NUM>) is started by loading the workpiece into an imaging system (e.g., the imaging system <NUM>). For example, the honeycomb body <NUM> can be loaded onto the part holder <NUM>.

At step <NUM>, the location of the workpiece is determined. In particular, the location of the honeycomb body <NUM> is determined relative to the imaging system <NUM>. In an example embodiment, the location of the honeycomb body <NUM> is determined by measuring the distance between the lens <NUM> and the honeycomb body <NUM>. The distance can be measured using the distance sensor <NUM> of imaging system <NUM>. The distance can be measured at a plurality of locations on the workpiece so that the angle of the end face of the workpiece relative to the optical axis of the lens <NUM> can be determined.

At step <NUM>, the workpiece is positioned relative to the camera (e.g., the camera <NUM> and/or its lens <NUM>) to provide desired alignment and positioning for imaging a portion of the workpiece. In an example, the honeycomb body <NUM> is positioned relative to the lens <NUM>, by translating it in an XY plane and by tilting it around the X-axis and/or Y-axis, so that a desired portion of the honeycomb body <NUM> is disposed in the field of view of the camera <NUM> and lens <NUM>. The honeycomb body <NUM> can be tilted so that the end face is normal to the optical axis of the lens <NUM> to improve imaging. The movement in the XY plane can correspond with the positions in the grid pattern illustrated in <FIG>. The honeycomb body <NUM> can be positioned relative to the lens <NUM> using any combination of movable stages, such as a movable stage <NUM> for the camera <NUM> and lens <NUM> and/or the movable stage <NUM>. The movable stages are selected so that the accuracy and repeatability of the relative position between the honeycomb body and the imaging system <NUM> is known within a predefined tolerance. As an example, the accuracy of the movable stage is selected so that a location of common features shown in adjacent images is known within a tolerance of half of a cell width. In another example embodiment, the accuracy of the movable stage is selected so that a location of common features shown in adjacent images is known within a <NUM> pixel tolerance. In this way, even if there is some error in movement, such that a feature is not exactly where expected, this feature can be still be identified since it is within a small degree of tolerance.

Step <NUM> can also comprise setting the relative Z-axis position between the workpiece and the imaging system to a distance that places the workpiece within the depth of field of the imaging system. In an example embodiment, the camera <NUM> and lens <NUM> are translated in a direction parallel to the Z-axis relative to the honeycomb body <NUM> by the movable stage <NUM>. That movement places an end face of the honeycomb body <NUM> in the depth of field of the lens <NUM> so that a portion of the honeycomb body <NUM> is in focus. The combination of movements provided in steps <NUM> and <NUM> effectively provide auto-levelling and auto-focus of the workpiece in the imaging system.

At step <NUM>, an image is captured. For example, the honeycomb body is illuminated and an image of at least a portion of the workpiece is captured. In an example embodiment, a processor (e.g., comprised by the controller <NUM>) determines that the honeycomb body is positioned in a desired position in the grid (e.g., has desired X- and/or Y-coordinates or indexes), directs the first and second light sources to illuminate the workpiece, and/or directs that camera <NUM> to capture an image of the honeycomb body <NUM>.

At step <NUM>, features of the workpiece are measured by analyzing the captured image. In other words, measurement data related to dimensions of features of the honeycomb body <NUM>, such as dimensions of the walls <NUM> and/or channels <NUM>, are extracted from the captured image. The image is used to identify the type, location, and dimensions of features of the honeycomb body <NUM>. Measurement data corresponding to the features of the honeycomb body <NUM> is compiled for each image. In an example embodiment, the honeycomb body <NUM> and imaging system <NUM> are stepped through the positions in the grid pattern, such as the grid pattern shown in <FIG>, and an image is captured at each position and analyzed.

At step <NUM>, the measurement data is converted into a common frame of reference using a common feature in an overlapping region between each adjacent pair of images so that the measurement data can be combined into a single measurement data set at step <NUM>. In this way, the combined measurement data set corresponds to the entire workpiece despite the measurement data being extracted from a plurality of images having different frames of reference. In an example embodiment, the measurement data can be normalized so that all of the measurement data corresponds to a single coordinate system and the normalized measurement data can be converted into a single frame of reference and combined together. In example embodiments, an image of the plurality of images can be selected to define a frame of reference that is used as a common frame of reference for all of the measurement data. Alternatively, a global frame of reference that is different than any frame of reference from the plurality of images can be used as a common frame of reference for all of the measurement data. Measurement data from adjacent images is collected, including measurement data applying to common features captured in the adjacent images. The common features permit measurement data taken from a plurality of images to be converted into the common frame of reference so that all of the measurement data can be combined into a single measurement data set.

The common features can be one or more features of the honeycomb body <NUM> that are captured in both images. The common features can be corner posts of a single cell, the centroid of a cell, centroids of a plurality of cells, etc., that are shown in an overlapping region between two images. The common feature can be measurements of a geometric imperfection, such as a bent wall, a discontinuous wall, a wall thickness anomaly, or another wall imperfection. Based on the common feature, a spatial relationship, such as a relative offset in X- and/or Y directions, between the images can be determined and can be used to convert measurement data from the reference frame of any image into the common frame of reference so that all of the measurements can be combined together into a single measurement data set based on the common frame of reference.

The identification of the common features can also be used to determine error in the positioning of the images relative to each other based on a predefined expected offset distance. For example, a measured location of a common feature in an image can be compared to an expected location of the common feature in that image based on a predefined expected offset to define an error in relative movement between the honeycomb body <NUM> and the imaging system <NUM> between capturing images. The predefined expected offset distance combined with any error can be used to define a spatial relationship between the images corresponding to a spatial relationship between the first frame of reference and the second frame of reference.

Additionally, a dimension between a plurality of common features in adjacent images can be used to determine an error, such as a scaling error. So, in line with claim <NUM>, the same dimension can be measured in each of the adjacent images to provide a first reference dimension and a second reference dimension. The measured values for the dimension are compared to determine if there is an error between the adjacent images, such as a scaling error. If there is no error, the first reference dimension and the second reference dimension are the same. However, if there is imaging error present, the reference dimensions will differ, and the difference can be used to define a transformation. The transformation can be applied to the measurement data to create converted measurement data that is normalized to the common frame of reference.

In an example embodiment, each image is analyzed to extract measurement data prior to moving to the next position, so that steps <NUM>, <NUM>, <NUM>, and <NUM> are repeated until the entire end face of the honeycomb body <NUM> is imaged and analyzed for measurement data. However, steps <NUM> and/or <NUM> need not occur immediately after step <NUM> for each image, but can instead the images and/or extracted measurement data can be saved (e.g., to data storage in the controller <NUM>) and analyzed at a later time.

Claim 1:
A method of measuring features of a workpiece comprising a honeycomb body (<NUM>) or a honeycomb extrusion die, the method comprising:
providing an imaging system (<NUM>);
capturing an image (<NUM>; <NUM>) of a first portion of the workpiece, wherein the image (<NUM>; <NUM>) of the first portion of the workpiece defines a frame of reference;
calculating a first plurality of measurements based at least in part on the image (<NUM>; <NUM>) of the first portion of the workpiece;
capturing an image (<NUM>; <NUM>) of a second portion of the workpiece, wherein the first portion of the workpiece and the second portion of the workpiece comprise a plurality of common features, wherein the second portion comprises at least one feature that is not included in the first portion of the workpiece;
calculating a second plurality of measurements based at least in part on the image (<NUM>; <NUM>) of the second portion of the workpiece, characterized in that the first and second pluralities of measurements correspond to dimensions of intersecting walls of the honeycomb body (<NUM>) or of intersecting slots of the honeycomb extrusion die, wherein at least one of the first plurality of measurements is a first reference dimension (R1) defined by the common features, wherein at least one of the second plurality of measurements is a second reference dimension (R2) defined by the common features, wherein the first reference dimension (R1) is defined by a dimension between the common features based at least in part on the image (<NUM>; <NUM>) of the first portion of the workpiece and the second reference dimension (R2) is defined by the same dimension between the common features based at least in part on the image (<NUM>; <NUM>) of the second portion of the workpiece;
comparing the first reference dimension (R1) to the second reference dimension (R2) to calculate a transformation;
applying the transformation to the second plurality of measurements to convert the second plurality of measurements into the frame of reference; and
combining the first plurality of measurements and the converted second plurality of measurements.