Patent Description:
Material processing systems relying on an energy beam to modify characteristics of a workpiece (e.g., additive manufacturing apparatuses, laser welding devices, laser cutting devices, or the like) may direct energy beams in predetermined patterns to generate material modifications (e.g., melt or fuse a portion of material) having a desired shape. To ensure that the energy beam produces desired material modifications in the workpiece, information regarding various aspects of the energy beam (e.g., beam shape and energy density profile) where the energy beam interacts with the workpiece is needed. For instance, if the material processing system directs the energy beam to the workpiece using an optical system, generation of the predetermined patterns based on an inaccurate focal position of the optical system may lead to undesired material modifications because the energy beam may lack the requisite energy density to modify a workpiece in an intended manner.

Certain material processing systems may include elements that introduce other directionally-dependent characteristics (e.g., beam geometry) into the energy beam. Such directionally-dependent characteristics may also alter the energy beam's ability to modify a workpiece and therefore should be accounted for to ensure that directing the energy beam in a particular pattern modifies the workpiece as intended. Related prior art comprises <CIT> and <CIT>.

According to an embodiment of the present disclosure, a method of characterizing an optical system of a laser processing system includes directing an energy beam through a plurality of portions of a sample by adjusting an orientation of an adjustable beam redirection element of the optical system in accordance with a predetermined movement pattern to form a plurality of test patterns in the sample at each portion. The optical system comprises an imaging system having an expected focal position. In the movement pattern, the energy beam is directed in a plurality of different directions in the sample in the formation of each test pattern. At least two of the plurality of test patterns are formed at different calibration distances from an expected focal position of the optical system. An accuracy of the expected focal position is determined by detecting a level of modification in the sample caused by the energy beam at the plurality of test patterns.

In another embodiment of the present disclosure, a method of determining a focal position of an optical system of a laser processing system includes positioning a sample a plurality of different distances of a distance range from the optical system. The distance range includes an expected focal position of the optical system. For each distance, an energy beam is directed through a separate portion of the sample in a predetermined movement pattern using an adjustable beam redirection element of the laser processing system to form a plurality of test patterns in the sample at each portion. The movement pattern includes a plurality of movements such that the energy beam is directed in a plurality of different directions in the sample in the formation of each test pattern. The method includes inspecting the plurality of test patterns to determine whether the expected focal position matches or substantially matches an actual focal distance of the optical system.

In another embodiment of the present disclosure, a laser processing system includes an energy beam source configured to emit an energy beam, an adjustable beam redirection element configured to direct the energy beam towards a support platform based on a configuration of the adjustable beam redirection element, and a support platform actuator coupled to the support platform. The support platform actuator is movable in a direction to adjust a distance between the support platform and the adjustable beam redirection element. The laser processing system also includes an optical system disposed between the energy beam source and the support platform, the optical system having a focal position where an energy density of the energy beam is a maximum. The laser processing system also includes a detector having a field of view that captures the support platform and a controller communicably coupled to each of the adjustable beam redirection element, the support platform actuator, and the detector. The controller is configured to direct the support platform to move to a plurality of distances of a distance range from the adjustable beam redirection element. The distance range includes an expected focal position of the optical system. The controller is also configured to cause the adjustable beam redirection element to direct the energy beam through a separate portion of a sample, for each of the plurality of distances, placed on the support platform in a predetermined movement pattern to form a plurality of test patterns in the sample at each portion. The predetermined movement pattern comprises a plurality of movements such that the energy beam is directed in a plurality of different directions in the sample in the formation of each test pattern. The controller is also configured to: capture an image containing the plurality of test patterns using the detector; and analyse the image to determine an accuracy of the expected focal position based on an amount of material modification in the sample at each of the plurality of test patterns.

Additional features and advantages of the processes and systems described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, comprising the detailed description which follows, the claims, as well as the appended drawings.

The accompanying drawings are comprised to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification.

Reference will now be made to systems and methods for characterizing a laser processing system as a function of beam position based analyzing a plurality of test patterns formed with multi-directional movement patterns of an energy beam. In various embodiments, the energy beam is directed through a plurality of portions of a sample using a predetermined multi-directional movement pattern for an adjustable beam redirection element of a laser processing system to form the plurality of test patterns. Between formation of the test patterns, the positioning of the sample may be changed such that each test pattern may be formed at a different calibration distance from an expected focal position of an optical system of the laser processing system. In embodiments, each of the test patterns is formed at a different calibration distance within a calibration distance range containing the expected focal position. For example, a first test pattern may be formed at a first calibration distance on a first side of the expected focal position, a second test pattern may be formed at the expected focal position, where the calibration distance is equal to zero, and a third test pattern may be formed at a second calibration distance on a second side of the expected focal position. The second calibration distance may equal the first calibration distance such that the expected focal position is centered in the calibration distance range. The calibration distance range in the preceding example may be expanded to include any number of test patterns (e.g., equal numbers of test patterns on either side of the expected focal position). After the formation of the test patterns, the test patterns may be compared (e.g., either directly by a user or through image analysis) to determine an accuracy of the expected focal position based on a level of material modification induced by the energy beam in each of the test patterns.

The multi-directional movement patterns described herein beneficially facilitate the characterization of several beam-modifying aspects of laser processing systems that are not characterized through existing techniques. For example, certain laser processing systems may include imaging optics that introduce an ellipticity into a beam shape of a laser beam. Such ellipticity may impact an amount of laser energy deposited in the sample along particular movement directions of the laser beam. As such, the laser beam's ability to modify the sample in a desired manner along a movement direction may depend on the direction that the laser is being directed via the adjustable beam redirection element. Additionally, laser processing systems may include optical systems possessing aberrations (e.g., astigmatism) that cause other directional dependencies (e.g., beam waist location or focal position) of the laser beam. Such additional directional dependencies may also impact the laser beam's ability to modify samples.

The multi-directional movement patterns described herein account for directional dependencies when calibrating laser processing systems, thus providing a more complete characterization of the laser processing system as a function of beam movement direction and position than conventional characterization methods. In embodiments, the multi-directional movement patterns described herein include at least two portions that extend at angles relative to one another such that the directional dependencies of the laser processing system are taken into account when forming the test patterns. In embodiments, the at least two portions that extend at angles relative to one another can include different lines such that an orientation of the energy beam's energy density cross-section with respect to the movement direction in each line changes. In embodiments, the at least two portions that extend at angles relative to one another are different segments of a non-linear curve such that the orientation of the energy beam's energy density cross-section with respect to the movement direction changes along the non-linear curve. As a result, the test patterns described herein incorporate changes in beam energy density resulting from movement direction dependences, providing a more complete characterization and calibration of the laser processing system.

Referring now to <FIG>, a laser processing system <NUM> is depicted in accordance with an example embodiment. The laser processing system <NUM> depicted in <FIG> is an additive manufacturing apparatus that builds objects or portions of objects, for example, the object <NUM>, in a layer-by-layer manner by sintering or melting a build material (e.g., a powder, not depicted) using an energy beam <NUM> generated by an energy beam source <NUM>. In embodiments, the energy beam source <NUM> is a laser and the energy beam <NUM> is a laser beam. In embodiments, the energy beam source <NUM> is a filament and current source, and the energy beam <NUM> is an electron beam. In embodiments where the energy beam <NUM> is a laser beam, the energy beam <NUM> sinters or melts a cross sectional layer of the build material under control of an optical system <NUM>.

The optical system <NUM> may include an imaging system <NUM> and an adjustable beam redirection element <NUM>. In the example depicted, the adjustable beam redirection element <NUM> is a galvo scanner that may include a plurality of movable mirrors or scanning lenses. In an embodiment, the adjustable beam redirection element <NUM> includes a first scanning mirror (not depicted) rotatably adjustable in a first direction (e.g., the x-direction) such that a first scanning angle Θ<NUM> is adjustable so the energy beam <NUM> may be scanned to cover an entirety of the build platform <NUM> in the first direction. The adjustable beam redirection element <NUM> may also include a second scanning mirror (not depicted) rotatably adjustable in a second direction (e.g., the y-direction) such that the energy beam <NUM> may be scanned to cover an entirety of the build platform <NUM> in the second direction. By adjusting the adjustable beam redirection element <NUM> in predetermined movement patterns, corresponding patterns in the build material may be modified (e.g., cured, melted, sintered) to produce the object <NUM>. In embodiments, the speed which the energy beam <NUM> is moved is a controllable process parameter that impacts the quantity of energy delivered to a particular spot. Typical energy beam movement speeds are on the order of <NUM> to several thousand millimetres per second.

In embodiments, the imaging system <NUM> focuses the energy beam <NUM> to deliver a required energy density to a build surface <NUM> such that the build material is modified in a desired manner. While the imaging system <NUM> is depicted as being upstream of the adjustable beam redirection element <NUM>, it should be appreciated that the imaging system <NUM> may be placed anywhere between the energy beam source <NUM> and the object <NUM> consistent with the present disclosure. As each layer of the object <NUM> is formed via the optical system <NUM>, the relative distance between a build platform <NUM> and the optical system <NUM> is changed (e.g., the build platform <NUM> may be lowered) and an additional layer of the object <NUM> is formed (e.g., via a recoater <NUM> forming an additional layer of powder at the build surface <NUM> in a recoater direction <NUM>, with any excess powder being pushed to a powder reservoir <NUM>). For example, after the build platform <NUM> is lowered, another layer of build material may be spread over the build platform <NUM> and the object <NUM>. The additional layer of build material may modified by moving the energy beam <NUM> in another pattern via the optical system <NUM> to form the additional layer of the object.

The energy beam <NUM> may be controlled by a computer system including a processor and a memory (not depicted). The computer system may determine a scanning pattern for each layer and control energy beam <NUM> to irradiate the build material according to the scanning pattern. After fabrication of the object <NUM> is complete, various post-processing procedures may be applied to the object <NUM>. Post-processing procedures include removal of excess powder by, for example, blowing or vacuuming. Other post processing procedures include a stress relief heat treat process. Additionally, thermal and chemical post processing procedures can be used to finish the object <NUM>.

In order to produce an object <NUM> having a desired shape, movement patterns for the energy beam <NUM> are determined based on an energy density profile of the energy beam <NUM> at the build surface <NUM>. For example, certain build materials may require a threshold energy density to be modified (e.g., melted, sintered, or the like) and eventually hardened for incorporation into the object <NUM>. The energy density profile of the energy beam <NUM> is typically non-uniform. For example, in embodiments, the energy density profile may be possess a Gaussian or other statistical distribution, having a variable energy density profile that gradually decreases from a maximum energy density in a central portion of the energy beam <NUM>. As such, only a portion of the energy beam <NUM> (e.g., immediately surrounding a center of the energy beam <NUM>) may possess the requisite energy density to sufficiently modify the build material for incorporation into the object <NUM>. The portion of the energy beam <NUM> possessing sufficient energy density to modify the build material may change as a function of position on the build platform <NUM> (e.g., as a function of scanning angle Θ<NUM>) due to impacts on the energy density profile of the energy beam <NUM> induced by the imaging system <NUM>. For example, astigmatism of the imaging system <NUM> may create a directional dependency of the beam waist (e.g., focal position, a position of maximum energy density) of the energy beam <NUM>. A focusing position of the optical system <NUM> may have a first value at a home position <NUM> of the optical system <NUM> and a second value that is different from the first value at some angle Θ<NUM> from the home position <NUM>.

<FIG> depicts a chart <NUM> showing a plurality of energy density cross-sections for the energy beam <NUM> for a plurality positions relative to a focal position of the optical system <NUM>. In embodiments, the energy density cross-section <NUM> depicted may correspond to an energy density cross-section of the energy beam <NUM> at the home position <NUM> of the optical system <NUM>, while the energy density cross-section <NUM> depicted may correspond to an energy density cross section at an angle Θ<NUM> from the home position <NUM>. As shown, the energy density cross-section <NUM> covers a much smaller area than the energy density cross-section <NUM> at some distance (e.g., about <NUM>, about <NUM>, about <NUM>, about <NUM>, etc.) from the focal position. Given this, the energy beam <NUM> may not possess the requisite energy density to modify the build material for incorporation into the object <NUM> in a desired pattern if the movement patterns of the adjustable beam redirection element <NUM> do not take such a directional dependency of the focusing position of the optical system <NUM> into account. As such, prior to programming the movement patterns for adjustable beam redirection element <NUM> to create a particular object <NUM>, it is beneficial to calibrate the laser processing system <NUM> to ensure the optical system <NUM> provides adequate energy density to the build surface <NUM> for each position of the adjustable beam redirection element <NUM>.

In embodiments, the energy density cross-section <NUM> possesses a substantially elliptical shape. In embodiments, the ellipticity of the energy beam <NUM> may depend on the orientation of the adjustable beam redirection element <NUM>. For example, as depicted in <FIG>, the energy density cross-section <NUM> possess a greater degree of ellipticity than the energy density cross-section <NUM>. Such a directionally-dependent ellipticity may further complicate calibration of the laser processing system <NUM>. For example, as depicted in <FIG>, a first energy density cross-section <NUM> of the energy beam <NUM> may possess a first orientation relative to a first movement direction <NUM> for the adjustable beam redirection element <NUM> (e.g., a first line of a movement pattern) and the second energy density cross-section <NUM> may possess a second orientation relative to a second movement direction <NUM> for the adjustable beam redirection element <NUM> (e.g., a second line of a movement pattern). The second energy density cross-section <NUM> is substantially elliptical and has a major axis that is substantially aligned with the second movement direction <NUM>. The first energy density cross section <NUM> contrasts with the second energy density cross-section <NUM> in that the major axis of the first energy density cross section <NUM> is not aligned with the first movement direction <NUM>, but rather rotated with respect to the first movement direction <NUM>. As a result, the average energy density of the energy beam <NUM> applied along the first movement direction <NUM> is smaller than the average energy density of the energy beam <NUM> applied along the second movement direction <NUM>. Given this, the mismatch in alignment between the first movement direction <NUM> and the first energy density cross-section <NUM> may result in an insufficient energy density being applied to sufficiently modify the build material along the first movement direction <NUM> for incorporation into the object <NUM>.

With the foregoing in mind, the laser processing system <NUM> may be calibrated in accordance with the methods described herein. Samples of test material may be placed at various locations on the build platform <NUM>. In embodiments, the test material may differ from the build material used to build the object <NUM>. For example, in embodiments, the test material is a metallic foil that is burned or ablated by the energy beam <NUM> when the energy beam <NUM> possesses a sufficient energy density. As described herein, various portions of the test samples may be modified by moving the energy beam <NUM> in a predetermined movement pattern via the optical system <NUM> to generate test patterns at each of the portions in the test samples. The predetermined movement pattern may include a plurality of movement directions for the adjustable beam redirection element <NUM> to incorporate directional dependencies of the energy density cross section of the energy beam <NUM> at various locations (e.g., relative to the home position <NUM>) on the build platform <NUM>. Various ones of the test patterns may be formed with the build platform <NUM> and optical system <NUM> being placed at different relative distances from one another (e.g., in the z-direction). An analysis and assessment of the plurality of test patterns formed in the samples of test material may be used to determine a focal position for the optical system <NUM> at various locations on the build platform (e.g., away from the home position <NUM>). Additionally, the analysis and assessment of the plurality of test patterns formed in the samples of test material may be used to form a calibration model of the optical system <NUM> mapping where in three-dimensional space the energy beam <NUM> possesses a sufficient energy density to form a complete test pattern in the samples of test material. Such a calibration model may be used to determine movement patterns used by the optical system <NUM> to build objects <NUM> after the calibration.

Referring to <FIG>, a laser processing system <NUM> under a calibration process is schematically depicted. The laser processing system <NUM> includes an energy beam source <NUM> that produces an energy beam <NUM>. In embodiments, the energy beam source <NUM> is a laser and the energy beam <NUM> is a laser beam. The laser processing system <NUM> may be any laser processing apparatus (e.g., an additive manufacturing apparatuses, a laser welding device, a laser cutting device, or the like) utilizing the energy beam <NUM> to modify material (e.g., melt, ablate, fuse, sinter, or the like) disposed on a support platform <NUM> in any manner. Additional components of the laser processing system <NUM> may be depend on the particular purpose of the laser processing system <NUM> and are left out for the purposes of simplifying the discussion herein. For example, in embodiments, the laser processing system <NUM> may correspond to the laser processing system <NUM> described herein.

The laser processing system <NUM> also includes an optical system <NUM> including an imaging system <NUM> and an adjustable beam redirection element <NUM>. The imaging system <NUM> may include various elements (e.g., lenses, mirrors, or the like. ) to focus the energy beam <NUM> on the support platform <NUM>. While the imaging system <NUM> is shown to be disposed between the energy beam source <NUM> and the adjustable beam redirection element <NUM>, it should be understood that the imaging system <NUM> may be disposed anywhere between the energy beam source <NUM> and the support platform <NUM>. The adjustable beam redirection element <NUM> may include at least reconfigurable element (e.g., a scanning mirror) such that the energy beam <NUM> may be moved throughout a range of motion <NUM> to illuminate an entirety of the support platform <NUM> (or a portion thereof). In embodiments, the adjustable beam redirection element <NUM> may be similar to the adjustable beam redirection element <NUM> described with respect to <FIG>.

The laser processing system <NUM> further includes a controller <NUM>. The controller <NUM> is communicably coupled to the adjustable beam redirection element <NUM>, a support platform actuator <NUM>, and a detector <NUM>. In embodiments, the controller <NUM> may be a controller associated with an intended mode of operation for the laser processing system <NUM>. In embodiments, the controller <NUM> may constitute a calibration controller that is separate from the laser processing system <NUM> and specifically used for the purpose of generating a calibration model for the laser processing system <NUM>. In embodiments, the controller <NUM> includes a memory storing executable instructions and a processor configured to execute the instructions to perform the calibration process described herein. For example, the controller <NUM> may include instructions configured to cause the adjustable beam redirection element <NUM> to move in predetermined multi-directional movement patterns for generating test patterns in a plurality of samples <NUM> disposed on the support platform <NUM>. In embodiments, the controller <NUM> includes instructions configured to cause the support platform actuator <NUM> to change a relative position of the support platform <NUM> with respect to the optical system <NUM> during the calibration process. For example, the support platform actuator <NUM> may move the support platform <NUM> throughout a range of calibration distances <NUM>.

In embodiments, the range of calibration distances <NUM> includes an expected focal position <NUM> of the optical system <NUM>. In embodiments, the expected focal position <NUM> may constitute a calculated focal distance of the imaging system <NUM> (e.g., based on an optical model) at the home position <NUM>. It should be understood that the expected focal position <NUM> depicted in <FIG> may correspond to a particular position of the energy beam <NUM> (e.g., the home position <NUM>). While the calibration process is described herein as taking place using a single expected focal position <NUM>, it should be understood that the process may take place using a number of different expected focal positions. For example, in embodiments, the calibration process may include a plurality of different expected focal positions, one for each sample <NUM> placed on the support platform <NUM> to account for directional variations in the focal position of the imaging system <NUM>. Any number of expected focal positions may be used to set any number of ranges of calibration distances in accordance with the present disclosure.

The energy beam source <NUM> may produce an energy beam <NUM> having an initial energy density cross-section. In embodiments, the imaging system <NUM> may modify at least one aspect of the initial energy density cross-section to form a modified energy density cross-section. In an example, the initial energy density cross-section may have a Gaussian profile and the imaging system <NUM> may modify the initial energy density cross-section such that the modified energy density cross-section has an elliptical profile. Additional aberrations (e.g., astigmatism) of the imaging system <NUM> may induce a directional dependency of a focal position of the imaging system <NUM>. For example, the focal position of the imaging system <NUM> may have a first value at a first position proximate to a home position <NUM> of the optical system <NUM> and have a second value at a second position (e.g., the position of the energy beam <NUM> depicted in <FIG>) further from the home position <NUM>. As a result, a size of the energy density cross-section of the energy beam <NUM> at the support platform <NUM> may depend on a position of the energy beam <NUM> relative to the home position <NUM>.

The calibration process described herein measures such aspects (e.g., the modified energy density profile, the directional dependency of focal position) of the laser processing system <NUM> to facilitate the generation of movement patterns for the energy beam <NUM> such that the energy beam <NUM> modifies material in an intended manner. When under the calibration process, a plurality of samples <NUM> are placed on the support platform <NUM>. As depicted in <FIG>, the samples <NUM> may be distributed throughout an entirety of the support platform <NUM> to characterize the energy beam <NUM> at a plurality of different positions on the support platform <NUM>. In embodiments, the samples <NUM> are arranged in a <NUM> x <NUM> array that covers the range of motion <NUM> of the energy beam <NUM> so that an accurate calibration model mapping where in three-dimensional space the energy beam <NUM> possesses the requisite energy density to form a complete test patterns in the samples <NUM>. It should be understood that any number of samples <NUM> may be placed on the support platform <NUM> and such samples <NUM> may be arranged in any manner consistent with the present disclosure.

The samples <NUM> may be constructed of any material capable of being modified by the energy beam <NUM> in a repeatable manner. In embodiments, the samples <NUM> are metal articles (e.g., a metal ingot, a three dimensional metal article such as a block, a metal plate, or the like). In embodiments, the samples <NUM> include metal articles and a powder layer (e.g., a metallic powder) disposed on a surface of the metal article. In embodiments, the samples <NUM> are metallic foil sheets that are melted when the energy beam <NUM> is incident on the samples with a requisite energy density. In embodiments, the samples <NUM> are constructed of laser paper, and the test patterns are burned areas on the samples <NUM>. In embodiments, if the energy beam <NUM> does not possess the requisite energy density, the samples <NUM> do not melt or burn but may be modified in a less conspicuous manner. In embodiments, the samples <NUM> are constructed of a material similar to that which the laser processing system <NUM> modifies in its normal course of operation. For example, if the laser processing system <NUM> is a laser cutting apparatus, samples <NUM> may include workpieces constructed from a material (e.g., glass, polymeric material, or the like) that the laser processing system <NUM> may cut once calibrated.

As depicted in <FIG>, during the calibration process described herein, a plurality of test patterns <NUM> are formed in each of the samples <NUM>. In the depicted example, each test pattern <NUM> in the plurality of test patterns <NUM> has the same shape (or is intended to have the same shape). In embodiments, each test pattern <NUM> in each of the samples <NUM> is formed at a different calibration distance in the range of calibration distances <NUM>. In other words, each test pattern <NUM> of the plurality of test patterns <NUM> formed in each sample <NUM> may be formed with the support platform <NUM> being disposed at a different relative distance from the imaging system <NUM>. In an example, a first one of the test patterns <NUM> in each of the samples <NUM> is formed at a first calibration distance <NUM> on a first side of the expected focal position <NUM> at a first end of the range of calibration distances <NUM> and a second one of the test patterns <NUM> in each of the samples <NUM> is formed at a second calibration distance <NUM> on a second side of the expected focal position <NUM> at a second end of the range of calibration distances <NUM>. In embodiments, the first and second calibration distances <NUM> and <NUM> are equidistant from the expected focal position <NUM>. A plurality of additional test patterns <NUM> are formed between the first and second test patterns formed at the first and second calibration distances <NUM> and <NUM>. For example, between forming each test pattern <NUM> of the plurality of test patterns <NUM> in each sample <NUM>, the controller <NUM> may provide a control signal to the support platform actuator <NUM> to cause the support platform actuator <NUM> to move the support platform <NUM> a predetermined increment (e.g., in the z-direction depicted in <FIG>). As such, in embodiments, each individual test pattern <NUM> of the plurality of test patterns <NUM> formed in each sample <NUM> may be formed at a separate calibration distance from the expected focal position <NUM>.

In embodiments, once the support platform <NUM> is positioned a desired calibration distance (e.g., within the range of calibration distances <NUM>) the controller <NUM> provides control signals to the adjustable beam redirection element <NUM> to provide relative motion of the energy beam <NUM> relative to the support platform <NUM>. For example, at the first calibration distance <NUM>, the orientation of the adjustable beam redirection element <NUM> may be moved to a starting point of one of the test patterns <NUM>. Once at the starting point, the controller <NUM> may control movements of the adjustable beam redirection element <NUM> such that the adjustable beam redirection element <NUM> moves in a predetermined movement pattern and the energy beam <NUM> is moved in a manner corresponding to the predetermined movement pattern to produce one of the test patterns <NUM>.

While the support platform <NUM> is still at the first calibration distance <NUM>, the controller <NUM> may orient of the adjustable beam redirection element <NUM> to another starting of another one of the test patterns <NUM> (e.g., another test pattern <NUM> at another one of the samples <NUM> disposed on the support platform <NUM>). Such a process may be repeated until a test pattern <NUM> has been formed at the first calibration distance <NUM> in each of the samples <NUM> disposed on the support platform <NUM>. Once a test pattern <NUM> is formed at the first calibration distance <NUM> in each of the samples <NUM>, the support platform actuator <NUM> may be repositioned to adjust the calibration distance within the range of calibration distances <NUM> and additional test patterns may be formed in each of the samples <NUM> at the updated calibration distance. In embodiments, such a process may be repeated until each of the samples <NUM> includes the same number of test patterns at a set of calibration distances within the range of calibration distances <NUM>. It should be understood that the movement pattern for the adjustable beam redirection element <NUM> and the support platform <NUM> is exemplary only and not meant to be limiting. For example, in embodiments, a plurality of test patterns <NUM> may be formed in an individual one of the samples <NUM> at a plurality of calibration distances prior to the energy beam <NUM> being repositioned to modify any of the other samples <NUM>. Moreover, each of the samples <NUM> may have different numbers of test patterns in the plurality of test patterns <NUM> formed therein and each of the plurality of test patterns <NUM> in each sample <NUM> may be formed used a different set of calibration distances and different calibration distance ranges consistent with the present disclosure.

In embodiments, the predetermined movement patterns for the adjustable beam redirection element <NUM> used to generate the test patterns <NUM> in the samples <NUM> are multi-directional to incorporate the directional-dependencies in the energy density cross-section of the energy beam <NUM> caused by the imaging system <NUM>. In embodiments, the predetermined movement patterns for the adjustable beam redirection element <NUM> contain at least two portions that extend at angles relative to one another. For example, in embodiments, the predetermined movement patterns are adapted to cause the energy beam to move in at two lines that extend at an angle relative to one another to account for an orientation of the energy density cross-section of the energy beam <NUM> being potentially misaligned with a movement direction of the energy beam <NUM> (e.g., as described herein with respect to <FIG>). More details with respect to movement patterns for the adjustable beam redirection element <NUM> are provided herein with respect to <FIG>, 6A, 6B, 6C, and 6D herein.

Still referring to <FIG>, the laser processing system <NUM> also includes a detector <NUM>. The detector <NUM> generates a calibration signal used to characterize the test patterns <NUM> formed in the samples <NUM> disposed on the support platform <NUM>. The nature of the calibration signal generated by the detector <NUM> may vary depending on the implementation. For example, in embodiments, the detector <NUM> may include a camera that captures images of each of the samples <NUM> having the plurality of test patterns <NUM> formed therein. In embodiments, a user of the laser processing system <NUM> may view the images captured via the detector <NUM> to determine an accuracy of the expected focal position <NUM> based on numbers of complete test patterns in each of the plurality of test patterns <NUM>. As described herein, each plurality of test patterns <NUM> may be formed using a set of a calibration distances within the range of calibration distances <NUM>. In embodiments, the expected focal position <NUM> is centrally disposed within the range of calibration distances <NUM> and the set of calibration distances is selected such that each plurality of test patterns <NUM> includes equal numbers of test patterns disposed on either side of the expected focal position <NUM>. In such a case, if the expected focal position <NUM> is accurate to a certain threshold, a number of complete test patterns on the first side of the expected focal position <NUM> (e.g., proximate to the first calibration distance <NUM>) should equal a number of complete test patterns on the second side of the expected focal position (e.g., proximate to the second calibration distance <NUM>).

As used herein, the term "complete test pattern" refers to a set of modifications to a sample that largely corresponds to a movement pattern of an energy beam. For example, if the adjustable beam redirection element <NUM> is adjusted to direct the energy beam <NUM> along a straight line having a predetermined length, a complete test pattern in this case would correspond to a sample <NUM> having a modification (e.g., melt pool) having a corresponding shape (e.g., the line having the predetermined length). If the energy beam <NUM> is out of focus and lacks the requisite energy density to modify the sample <NUM> in an intended manner such that the sample is not modified to possess a linear feature having the predetermined length, such a result is not characterized as a complete test pattern. In other words, if the energy beam <NUM> fails to modify the sample <NUM> in a desired manner at any point along a movement pattern for the energy beam <NUM>, an incomplete test pattern would result.

In embodiments, the controller <NUM> includes an imaging processing module or the like that causes the controller <NUM> to analyse the images captured via the detector <NUM> to determine whether each test pattern <NUM> is complete in an automated manner. For example, the imaging processing module may compare each test pattern to a baseline test pattern (e.g., formed at the expected focal position <NUM>) and determine that a particular test pattern <NUM> is complete if the shape of the test pattern <NUM> does not significantly differ the baseline test pattern. In embodiments, the controller <NUM> may count the number of test patterns characterized as complete on either side of the expected focal position <NUM> in order to determine whether the expected focal position is accurate. If there is a mismatch in the number of complete test patterns on either side of the expected focal position <NUM>, the controller <NUM> may update the expected focal position for a particular location on the support platform <NUM> (e.g., corresponding to the sample <NUM>) accordingly. For example, if a first number of complete test patterns on a first side of the expected focal position <NUM> is less than a second number of complete test patterns on a second side of the expected focal position <NUM>, the controller may update the expected focal distance to be disposed on the second side of the initial expected focal position <NUM>. This way, an expected focal position may be generated for various locations on support platform <NUM> to generate a calibration map for the laser processing system <NUM>.

In embodiments, the energy beam <NUM> melts each of the samples <NUM> when directed through various portions of the samples <NUM> using the predetermined movement patterns of the adjustable beam redirection element <NUM> to generate the plurality of test patterns <NUM>. The melting of the samples <NUM> may induce emissions <NUM>. For example, in embodiments, the emissions <NUM> are melt pool optical emissions. The detector <NUM> may include an optical detector that generates a detection signal responsive to the emissions <NUM> produced in the process of forming a particular test pattern <NUM> that may be used to determine a completeness of the test pattern <NUM>. For example, the detection signal may be compared to a signature response produced in forming a complete test pattern to determine a completeness of a particular one of the test patterns <NUM>.

In embodiments, the detector <NUM> is a temperature sensor that measures a temperature of a sample <NUM> during a time period immediately following the generation of a particular test pattern <NUM> in the sample <NUM>. For example, the detector <NUM> may determine a temperature of a laser heat affected zone (HAZ) of the sample <NUM> following the formation of a test pattern <NUM> to determine a completeness of the test pattern <NUM>. While only a single detector <NUM> is depicted, it should be understood that the laser processing system <NUM> may include any number of detectors consistent with the present disclosure. For example, in embodiments, the laser processing system <NUM> includes one detector for each sample <NUM> placed on the support platform <NUM> during the calibration process described herein to reduce the amount of time needed to measure the response corresponding to each test pattern <NUM>. In embodiments, the detector <NUM> (or each detector included in the laser processing system <NUM>) may be movable (e.g., coupled to an articulating arm or other actuator, not depicted) to capture the response corresponding to each test pattern <NUM> formed in the samples <NUM>.

Referring to <FIG>, a flow diagram of a calibration process <NUM> is depicted. In embodiments, the calibration process <NUM> may be performed via the laser processing system <NUM> described herein with respect to <FIG> to determine an accuracy for the expected focal position <NUM>. In embodiments, the calibration process <NUM> may be performed a single time to characterize the optical system <NUM> throughout an entirety of a range of motion <NUM> of the energy beam <NUM>. In embodiments the calibration process <NUM> may be performed to characterize the optical system <NUM> throughout only a portion of the range of motion <NUM> of the energy beam <NUM> (e.g., a portion of the range of motion <NUM> corresponding to one of the samples <NUM> depicted in <FIG>). In such embodiments, the calibration process <NUM> may be performed a number of different times to characterize the optical system <NUM> throughout the entirety of the range of motion <NUM>.

In a block <NUM>, a sample of test material is provided on the support platform <NUM> of the laser processing system <NUM>. For example, a plurality of samples <NUM> may be placed on the support platform <NUM> in a predetermined arrangement. The predetermined arrangement may be the grid-like arrangement depicted in <FIG>. The test material may be any material capable of being modified by the energy beam <NUM> in a repeatable and detectable manner. For example, in embodiments, the test material is a metal foil that is melted via the energy beam <NUM> when the energy beam <NUM> possesses a requisite energy density. In embodiments, the test material is modified via the energy beam <NUM> to enough of an extent such that the modifications (e.g., melt pools) in the test material induced by the energy beam <NUM> are visible (e.g., via a microscope of via a naked eye of a user).

In a block <NUM>, the support platform <NUM> is positioned a calibration distance from the expected focal position <NUM>. In embodiments, the calibration distance is a first calibration distance <NUM> on a first side of the expected focal position <NUM> at a first end of a range of calibration distances <NUM>. For example, the controller <NUM> may provide a control signal to the support platform actuator <NUM> to place the support platform <NUM> at a first relative distance from the imaging system <NUM> such that the sample <NUM> is placed the first calibration distance <NUM> from the expected focal position <NUM>.

In a block <NUM>, the energy beam <NUM> is directed through a portion of the sample <NUM> to form a test pattern. For example, the controller <NUM> may provide a plurality of control signals to the adjustable beam redirection element <NUM> to cause the adjustable beam redirection element <NUM> to direct the energy beam <NUM> in a predetermined movement pattern at the portion of the sample <NUM>. Depending on the energy density possessed by the energy beam <NUM> at the sample <NUM>, the energy beam <NUM> may modify the portion of the sample <NUM> to include a complete test pattern that corresponds in a shape of the movement pattern of the energy beam <NUM>. If the energy beam <NUM> lacks the requisite energy density to melt the sample <NUM> (e.g., because the energy beam <NUM> is out of focus at the sample <NUM>), an incomplete test pattern may result. In embodiments, after formation of a test pattern <NUM> in a first one of the samples <NUM>, the controller <NUM> may transmit a control signal to the adjustable beam redirection element <NUM> to cause the adjustable beam redirection element <NUM> to direct the energy beam <NUM> to a starting point of an additional test pattern. The additional test pattern may be formed in a portion of another sample <NUM> placed on the support platform <NUM>.

In a block <NUM>, the support platform <NUM> is moved to adjust the calibration distance. For example, the controller <NUM> may provide a control signal to the support platform actuator <NUM> to advance the support platform <NUM> from the calibration distance to which the support platform <NUM> was initially moved at block <NUM> in a predetermined increment (e.g., <NUM>, <NUM>, <NUM>, <NUM>, or the like). In a block <NUM>, the energy beam <NUM> is directed through another portion of the sample <NUM> to form an additional test pattern at the adjusted calibration distance. The adjusted calibration distance may alter the energy density of the energy density of the energy beam <NUM> to enough of an extent that the additional test pattern differs from the initial test pattern formed at block <NUM>. In embodiments, additional test patterns may be formed in other samples <NUM> placed on the support platform <NUM> at the adjusted calibration distance.

In a block <NUM>, the controller <NUM> determines whether a test pattern has been formed for a desired set of calibration distances. The set of calibration distances may vary depending on the implementation. For example, in embodiments, the set of calibration distances includes equal numbers of calibration distances on either side of the expected focal position <NUM> separated from one another by the predetermined increment. If a test pattern has not yet been formed for the desired set of calibration distances, the calibration process <NUM> reverts back to the block <NUM>, the calibration distance is adjusted, and an additional test pattern is formed.

If a test pattern has been formed for each calibration distance of the desired set of calibration distances, the calibration process advances to the block <NUM>, where the level of material modification in the test patterns is assessed to determine an accuracy of the expected focal position <NUM>. Referring to <FIG>, a sample <NUM> having different pluralities of test patterns 512a, 512b, 512c, 512d formed therein are schematically depicted, respectively. In embodiments, depending on the implementation, the sample <NUM> includes first pluralities of test patterns 502a, 502b, 502c, and 502d formed on a first side of the expected focal position <NUM> and a second plurality of test patterns 504a, 504b, 504c, and 504d formed on a second side of the expected focal position <NUM>.

The different shapes of the pluralities of test patterns 502a, 502b, 502c, 502d, 504a, 504b, 504c, and 504d represent the various movement patterns for the energy beam <NUM> that may be used in performance of the calibration process <NUM>. For example, each test pattern in the pluralities of test patterns 502a and 504a depicted in <FIG> includes a plurality of lines extending at acute angles relative to one another, such that the cross-section of energy beam <NUM> may be oriented differently relative to each of the lines. Each test pattern in the pluralities of test patterns 502b and 504b depicted in <FIG> is an octagonal shape comprising a plurality of connected linear segments extending at various angles to one another to test different relative orientations between cross-sectional shapes of the energy beam <NUM> and the scanning direction. Each test pattern in the pluralities of test patterns 502c and 504c depicted in <FIG> may be similar to the test patterns of the pluralities of test patterns 502a and 504a, except the lines intersect at centers thereof to form an asterisk pattern. Each test pattern in the pluralities of test patterns 502d and 504d is substantially circular-shaped such that the relative orientation between the cross-section of the energy beam <NUM> varies throughout the movement pattern of the energy beam <NUM>.

Each test pattern in the pluralities of test patterns 502a, 502b, 502c, 502d, 504a, 504b, 504c, and 504d may have differing levels of completion (e.g., different levels of correspondence between the test pattern produced in the sample <NUM> and the movement pattern of the energy beam <NUM> through that portion of the sample). For example, as depicted in each of <FIG>, each of the first pluralities of test patterns 502a, 502b, 502c, and 502a includes a first test pattern 506a, 506b, 506c, and 506d, respectively (e.g., formed at the first calibration distance <NUM> at the end of the range of calibration distances <NUM>), that is substantially incomplete and the sample <NUM> is hardly modified therein. Each of the first pluralities of test patterns 502a, 502b, 502c, and 502d further includes a second test pattern 508a, 508b, 508c, and 508d, respectively (e.g., formed at a calibration distance closer than the first calibration distance <NUM> within the range of calibration distances <NUM>), that is substantially more noticeable (e.g., the sample <NUM> is modified to a greater extent therein) than in the first test patterns 506a, 506b, 506c, and 506d. Each of the first pluralities of test patterns 502a, 502b, 502c, and 502a further includes a third test pattern 510a, 510b, 510c, and 510d, respectively (e.g., formed at a different calibration distance than the second test patterns 508a, 508b, 508c, and 508d), that is even more complete and noticeable than the second test pattern 508a, 508b, 508c, and 508d in that sample <NUM>.

Referring now to <FIG>, third test pattern 510a of <FIG> is depicted in more detail. The third test pattern 510a is a complete test pattern, and therefore largely corresponds in shape to the movement pattern of the energy beam <NUM> over that portion of the sample <NUM>. The test pattern 510a (and therefore the associated movement pattern of the energy beam <NUM> caused by the adjustable beam redirection element <NUM>) includes a first line <NUM>, a second line <NUM>, a third line <NUM>, and a fourth line <NUM>. In embodiments, the first line <NUM> extends along a first major scanning axis of the adjustable beam redirection element <NUM>. For example, the adjustable beam redirection element <NUM> may include a two axis galvo scanner having a first mirror rotatable to move the energy beam <NUM> along the first major axis (e.g., extending in the x-direction depicted in <FIG>) and a second mirror rotatable to move the energy beam <NUM> along a second major axis (e.g., extending the y-direction depicted in <FIG>). Combinations of movements of the first and second mirrors may move the energy beam along directions off the first and second major axes (e.g., along the third and fourth lines <NUM> and <NUM>). Inclusion of the first and second lines <NUM> and <NUM> in the test pattern beneficially characterizes the energy density of the energy beam <NUM> along the major axes (e.g., to test an effect of rotating an orientation of an elliptical energy density cross-section of the energy beam <NUM> with respect to the movement direction of the energy beam <NUM> as described herein with respect to <FIG>). For example, in embodiments, when scanned along the sample <NUM> to produce the first line <NUM>, the energy beam <NUM> may possess an elliptical cross-section having a major axis aligned with the movement direction of the energy beam <NUM> (e.g., similar to the second energy density cross-section <NUM> described with respect to <FIG>).

The third line <NUM> extends at a first acute angle <NUM> to the first line <NUM>. The fourth line <NUM> extends at a second acute angle <NUM> from the third line <NUM>. Inclusion of the third and fourth lines <NUM> and <NUM> extending at differing angles from the first line <NUM> facilitates taking different orientations of the energy density cross-section of the energy beam <NUM> with respect to the movement direction of the energy beam <NUM> into account. For example, referring back to <FIG>, in the second test pattern 508b, the first line <NUM> appears to be substantially complete and correspond to the first line <NUM> in the third test pattern 510a. However, the second, third, and fourth lines <NUM>, <NUM>, and <NUM> in the second test pattern 508a are substantially incomplete (e.g., the sample <NUM> is not modified to the same extent along the second, third, and fourth lines <NUM>, <NUM>, and <NUM> in the second test pattern 508a as compared to the third test pattern 510a). Such a difference between the second test pattern 508a and the third test pattern 510a may result from a misalignment of energy density cross-section of the energy beam <NUM> with the direction of movement along second, third, and fourth lines <NUM>, <NUM>, and <NUM>. While such misalignment may still be present during the production of the third test pattern 510a, the third test pattern 510a may be produced at a smaller calibration distance from the expected focal position <NUM>. As such, during generation of the third test pattern 510a, the energy beam <NUM> generally possesses a higher energy density than when generating the second test pattern 508a and thus generate a more complete test pattern.

Referring now to <FIG>, the third test pattern 510b of <FIG> is depicted in more detail. In embodiments, the third test pattern 510b is substantially complete, such that the sample <NUM> is modified in a manner that largely corresponds to the movement pattern of the energy beam <NUM>. As depicted, the third test pattern 510b is substantially octagonal-shaped, comprising a first set of segments <NUM> extending in a first direction (e.g., the Y-direction depicted in <FIG>) and a second set of segments <NUM> extending in a second direction (e.g., the X-direction depicted in <FIG>). In embodiments, the first and second sets of segments <NUM> and <NUM> extend along major scanning axes of the adjustable beam redirecting element <NUM> to test the material modification capability of the energy beam <NUM> along those axes. A third set of segments <NUM> connects the first and second sets of segments <NUM> and <NUM>. The third set of segments may extend at a first angle <NUM> to the second set of segments <NUM> and a second angle <NUM> to the first set of segments <NUM>. In embodiments, the first angle <NUM> equals the second angle <NUM> to form an octagonal shape, though various values for the first and second angles <NUM> and <NUM> may be chosen throughout the third test pattern 510b in order to test different relative orientations of the energy beam <NUM> and the movement direction thereof.

As exemplified by the preceding discussion, various multi-directional movement patterns of the energy beam <NUM> used in the calibration process <NUM>, such that that the calibration process <NUM> incorporates various directional dependencies of the energy density of the energy beam <NUM>, thus providing a more complete characterization of the ability of the energy beam <NUM> to modify the test material. Additionally, it should be appreciated that different movement patterns of the energy beam <NUM> may be used over a single iteration of the calibration process <NUM>.

In embodiments, to determine an accuracy of the expected focal position <NUM>, a user of the laser processing system <NUM> counts a number of complete test patterns formed on either side of the expected focal position <NUM>. In embodiments, the controller <NUM> may identify the numbers of complete test patterns through an image comparison algorithm. In the example depicted in <FIG>, the first plurality of test patterns 502a appears to include approximately <NUM> complete test pattern, whereas the second plurality of test patterns 504a appears to include approximately <NUM> complete test patterns. Such an imbalance indicates that an actual focal position of the optical system <NUM> is on the first side of the expected focal position <NUM>. In embodiments, based on the numbers of complete test patterns on each side of the expected focal position, the controller <NUM> may update the expected focal position. In embodiments, the calibration process <NUM> may be repeated using the updated expected focal position to determine an accuracy of the updated expected focal position.

Referring to <FIG>, a flow diagram of a calibration process <NUM> is depicted. In embodiments, the calibration process <NUM> may be performed via the laser processing system <NUM> described herein with respect to <FIG> to incorporate an expected focal position <NUM> of the optical system <NUM> into a calibration model of the laser processing system <NUM>. For example, the expected focal position <NUM> may be associated with a particular location on the support platform <NUM> (e.g., such that the energy beam <NUM> significantly deviates from the home position <NUM>). In embodiments, the process <NUM> may be repeated for a plurality of different locations on the support platform <NUM> to determine an accuracy of a plurality of expected focal positions of the optical system <NUM> and generate a three-dimensional calibration map for the optical system <NUM>.

In a block <NUM>, a sample of test material is provided on the support platform <NUM> of the laser processing system <NUM>. For example, a sample <NUM> may be placed on the support platform <NUM>. In embodiments, a plurality of samples <NUM> may be placed on the support platform <NUM> in a predetermined arrangement. The predetermined arrangement may be the grid-like arrangement depicted in <FIG>. The test material may be any material capable of being modified by the energy beam <NUM> in a repeatable and detectable manner. For example, in embodiments, the test material is a metal foil that is melted via the energy beam <NUM> when the energy beam <NUM> possesses a requisite energy density. In embodiments, the test material is modified via the energy beam <NUM> to enough of an extent such that the modifications (e.g., melt pools) in the test material induced by the energy beam <NUM> are visible (e.g., via a microscope of via a naked eye of a user).

In a block <NUM>, a plurality of test patterns are formed in a plurality of portions of the sample. For example, in embodiments, the block <NUM> may correspond to the blocks <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> of the calibration process <NUM> described with respect to <FIG> such that a plurality of test patterns are formed at various portions of the sample <NUM> at various different calibration distances from an expected focal position of the optical system <NUM>. To form each test pattern, the energy beam <NUM> may be moved in a multi-directional movement pattern described herein.

In a block <NUM>, an accuracy of the expected focal position of the optical system <NUM> is determined based on the plurality of test patterns formed at block <NUM>. In embodiments, during the block <NUM>, the controller <NUM> may analyse an image (e.g., similar to the image of the sample <NUM> described with respect to <FIG>) to determine numbers of complete test patterns disposed on either side of the expected focal position to assess the accuracy of the expected focal position. In embodiments, additional aspects of the test patterns may be assessed in determining the accuracy of the expected focal position. For example, in embodiments, the detector <NUM> may measure emissions from a melt pool (e.g., when the samples <NUM> are metal articles) by generating detection signals by measuring the emissions <NUM> (e.g., infrared components thereof) during the formation of the plurality of test patterns. In embodiments, a camera (e.g., co-located with the detector <NUM> and/or incorporated with the detector <NUM>) captures images of melt pools during the formation of the plurality of test patterns. In embodiments, after the plurality of test patterns are formed, the samples <NUM> are divided into at least one section (e.g., a cross-section extending through at least a portion of the plurality of the test patterns and extending perpendicular to the movement directions of the energy beam <NUM> in the plurality of movement patterns). After division into the at least one section, the samples <NUM> may be polished, and examined under a microscope to measure the melt or burn cross-section of the plurality of test patterns in assessing the completeness of the test pattern or the accuracy of the expected focal position.

In a block <NUM>, the controller <NUM> determines if the expected focal position is accurate to a threshold. For example, if the numbers of complete test patterns on either side of the expected focal position are not substantially equal (e.g., are equal or differ from one another by less than a threshold such as <NUM>), the controller <NUM> may determine that the expected focal position is not accurate and adjust the expected focal position in a block <NUM>. In embodiments, after adjusting the expected focal position, the calibration process <NUM> may be repeated to determine an accuracy of the adjusted expected focal position.

In embodiments, if the numbers of complete test patterns on either side of the expected focal position are substantially equal (e.g., are equal or differ from one another by less than a threshold such as <NUM>), the controller <NUM> determines that the expected focal position is sufficiently accurate and incorporates the expected focal position into a calibration model for the laser processing system <NUM>. For example, the expected focal position may be associated with a particular location (e.g., a position of the center of the sample <NUM> when the test patterns were formed during the block <NUM>) on the support platform <NUM> and used in the process of forming various movement patterns for the energy beam <NUM> for processing future workpieces.

Claim 1:
A method (<NUM>) of characterizing an optical system (<NUM>) of a laser processing system (<NUM>), the method (<NUM>) comprising:
directing an energy beam (<NUM>) through a plurality of portions of a sample (<NUM>) by adjusting an orientation of an adjustable beam redirection element (<NUM>) of the optical system (<NUM>,<NUM>) in accordance with a predetermined movement pattern to form a plurality of test patterns (<NUM>) in the sample (<NUM>) at each portion, wherein:
the optical system (<NUM>,<NUM>) comprises an imaging system (<NUM>,<NUM>) having an expected focal position (<NUM>),
the movement pattern comprises a plurality of movements such that the energy beam (<NUM>) is directed in a plurality of different directions in the sample (<NUM>) in the formation of each test pattern, and
at least two of the plurality of test patterns (<NUM>) are formed at different calibration distances from an expected focal position of the optical system (<NUM>,<NUM>); and
determining an accuracy of the expected focal position of the imaging system (<NUM>,<NUM>) by detecting a level of modification in the sample (<NUM>) caused by the energy beam (<NUM>) at the plurality of test patterns (<NUM>), wherein determining the accuracy of the expected focal position comprises:
capturing an image of the sample (<NUM>) containing the plurality of test patterns (<NUM>) using a detector (<NUM>); characterised in that processing the image using a controller communicably coupled to the detector (<NUM>) in order to determine a completeness of at least one of the plurality of test patterns (<NUM>).