Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Programme-control systems
  • G05B19/02—Programme-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
  • G05B19/182—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by the machine tool function, e.g. thread cutting, cam making, tool direction control
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T7/00—Image analysis
  • G06T7/70—Determining position or orientation of objects or cameras
  • G06T7/73—Determining position or orientation of objects or cameras using feature-based methods
  • G06T7/74—Determining position or orientation of objects or cameras using feature-based methods involving reference images or patches
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N1/00—Sampling; Preparing specimens for investigation
  • G01N1/02—Devices for withdrawing samples
  • G01N1/04—Devices for withdrawing samples in the solid state, e.g. by cutting
  • G01N2001/045—Laser ablation; Microwave vaporisation
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/50—Machine tool, machine tool null till machine tool work handling
  • G05B2219/50057—Compensation error by probing test, machined piece, post or pre process
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/30—Subject of image; Context of image processing
  • G06T2207/30108—Industrial image inspection
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J49/00—Particle spectrometers or separator tubes
  • H01J49/02—Details
  • H01J49/04—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components
  • H01J49/0459—Arrangements for introducing or extracting samples to be analysed, e.g. vacuum locks; Arrangements for external adjustment of electron- or ion-optical components for solid samples
  • H01J49/0463—Desorption by laser or particle beam, followed by ionisation as a separate step

Definitions

• Analysis systems such as mass spectrometry (MS) systems, optical emission spectrometry (OES) systems and the like, can be used to analyze the composition of a target material, for example a solid crystal.
• a sample of the target is provided to analysis systems of this type in the form of an aerosol.
• the aerosol is typically produced by arranging the target material in a sample chamber, introducing a flow of a carrier gas within the sample chamber, and ejecting a portion of the target in the form of particles.
• the ejecting may be done for example by laser ablating a portion of the target with one or more laser pulses, from a laser, to generate a plume containing particles and/or vapor ejected or otherwise generated from the target suspended within the carrier gas. Thereafter, the ejected particles are typically entrained by the flowing carrier gas and transported to an analysis system via a sample transport conduit.
• analysis systems perform applications including Laser ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Laser ablation Inductively Coupled Plasma Optical Emission Spectrometry (LA-ICP-OES)
• XYZ XYZ, positioning system during experimental runs performed subsequently to a scan placement process in which movements to be repeated during the experimental run are set.
• One exemplary use of analytical laser ablation systems is for zircon crystal grain dating. Zircon crystals incorporate uranium and thorium atoms into the crystalline structure, and strongly reject lead during the formation of the crystal. Therefore, any lead present in a zircon crystal is assumed to be from radioactive decay. Therefore, if the composition of a zircon crystal is determined the age of the crystal can be determined by calculating the amount of time it would take to produce the ratio of uranium to lead in the crystal through radioactive decay.
• invisible structures may exist that can be imaged using an SEM, XRF or other similar tool. These invisible structures may cause areas of a crystal grain to be not ideal for certain analytical laser ablation applications.
• a desired target on a zircon crystal grain for zircon crystal dating, and similar applications may be a very small and thus these applications require very high precision for ablating a surface of a crystal grain, and therefore require high precision stage movement.
• an exemplary sample slide may be prepared containing approximately 20-200+ grains in an approximately 50mm by 50mm area.
• the grains may be placed on the slide automatically or by a user.
• the grains may be placed in a random arrangement or in an orderly pattern, such as in rows and columns. Further, the grains may be placed according to sets of crystal grains to be analyzed together. After placement the grains may be machined to have flat surfaces substantially on the same plane as the other grains on the sample slide.
• sample slide After the sample slide is prepared it is loaded into a sample chamber of an analytical laser ablation device and a scan placement process is performed.
• An operator places a pattern scan, also referred to as an overlay, on the sample slide. This may be done with using software to perform a virtual overlay of pattern shapes.
• locations of a series of scans or holes to be fired upon by the laser are set in precise positions, for example at specific locations on the machined faces of individual crystal grains. These set positions are referred to as intended laser locations.
• intended laser locations Once the scan placement process is complete an experimental run occurs where a motion control system executes a series of movements determined by the scan placement process to ablate each crystal grain at the intended laser locations at a desired time and sequence.
• a reference material blank is usually placed in the sample chamber of a laser ablation apparatus, such as off to one side of the main experiment area.
• the reference blank has a known composition.
• the system may be set to analyze sets of zircon crystals grains and between sets of zircon crystal grains the system will then be programmed to sample the reference blank material. In this way, analytical drifts measured at an ICP-MS for example can be corrected for given the reference's known and repeatable concentrations of material.
• XY, or XYZ, stage coordinates During the experimental run, for each intended laser location the sample is moved relative to the laser by the motion control system according to the saved coordinate position. [0009] During an experimental run a motion control system will move the sample slide relative to the laser for each incrementally setup intended laser location on a zircon crystal grain in a set in the sample and then to the reference blank, then back to the next set of crystal grains. With each large movement either between crystal grains with intended laser locations, or to the reference blank a bi-directional repeatability error may appear to shift the sample slide relative to the laser beam's position. A large 30mm move can incur a built up bi-directional repeatabilty or accuracy error that will shift the laser focus position off of the intented laser position on a crystal grain.
• the precision with which the ablation pattern was placed relative to the sample will be reduced by the time the laser is to be fired if a repeatability error accumulates.
• the laser will fire in an unintended location, including missing the crystal grain with an intended laser location thereon altogether. This is undesirable since a laser firing at an unintended location will skew or ruin the data for that experiment pass.
• Open loop designs may be stepper motor based, and move the stage via linear type motors or lead-screw drive type mechanisms a precise amount , for example a fraction of the actual full step range.
• Each step can be on the order of l-2um of XY movement, with microstepping adding a divide by 2,4,8,16 or 32 microsteps per full step. In this way it is possible to attempt positioning at a very high resolution, only limited by the mechanical coupling of the stage mechanism.
• Closed loop adds to this a feedback mechanism and a controller topology that attempts to reduce requested position-actual position error until the error is zero or very small.
• Embodiments of the present invention relate generally to saving XYZ stage coordinates for intended laser locations as well as a kernel image of an ablation pattern placed during a scan placement process, and comparing the kernel image to a current image of the current field of view of a camera/microscope that includes the location a laser would be fired at. This comparision is used during an experiemental run to correct for any built up error. More particularly, embodiments of the present invention relate to apparatuses and methods for software based image recognition to correct errors in open looped systems for positioning a sample relative to a laser in analysis systems for zircon crystal grain dating. Brief Description of the drawings
• Fig. 1 is a cross sectional view of a laser ablation apparatus.
• Fig. 2 illustrates a sample slide containing zircon crystal grains.
• Fig. 3 is a flow chart diagram.
• Figs. 4a-c illustrate the field of view of a camera/microscope during the scan placement and experimental run steps.
• FIG. 1 illustrates a cross sectional view of a laser ablation apparatus 100.
• Laser ablation apparatus 100 includes a laser 101, a camera/microscope 102 fixed relative to the laser 101, a sample chamber 103, and a motion control system 104 which controls movements of the sample chamber 103 relative to the laser 101 and camera/microscope 102.
• a sample slide 105 is placed within the sample chamber 103.
• the sample chamber includes an inlet conduit 106 to allow in a flow of carrier gas and a sample transport conduit 107 to allow the exit of carrier gas.
• a reference blank 108 which may be separate or integral with the sample slide 105.
• Fig. 2 illustrates a sample slide 105 and a zoomed in view 201 of a portion of the surface of the slide.
• each crystal is machined to have a flat surface 204.
• Embodiments of the invention include software based image recognition to correct errors that tend to shift the sample relative to the laser beams during an experimental run. In embodiments, this is done by precisely moving a stage of a motion control system to the intended laser location of an ablation pattern set during a scan placement process. This precise movement is accomplished by comparing images saved during the scan placement process as kernel image with current position images of the camera/microscope field of view and calculating corrective moves.
• the xyz position in combination with a kernel image will ensure the laser fires precisely at the intended laser locations that were set during the scan placement process by correcting for any movement error incurred when returning to an intended laser position that was set during the scan placement process.
• movement error is less than half the field of view of the camera/microscope , for example 350um, ensuring that the intended laser location is close enough to appear in the field of view of the camera/microscope view during the experimental run. This current camera/microscope view is then used to compare against the saved kernel image location, and an XY, or XYZ, offset move can be applied to correct for the error.
• Fig. 3 is a flow chart diagram of an embodiment.
• the process begins 301 and an ablation pattern is placed onto a sample in a first step 302, for example using software to perform a virtual overlay of pattern shapes.
• the virtual overlay software using the field of view of the camera/microscope 102 allows a user to view a portion of the sample slide containing a crystal grain 202 and set an intended laser position for a location on a crystal grain.
• the virtual overlay software further allows a user to set the intended laser positions on a plurality of crystal grains 202 on the sample slide 105 forming an ablation pattern.
• An embodiment of setting an intended laser location on a crystal grain is illustrated in Fig.
• FIG. 4A showing a field of view of the camera/microscope 102 with crosshairs and a spot representing an intended laser location 401 for a laser to be fired onto a zircon crystal grain 202 located in the field of view.
• this information includes XY, or XYZ, positions.
• firing information and movement properties are saved.
• a user continues setup of the remaining experiment 303, comprising multiple movements and/or initiation of an experimental scan of the placed pattern(s).
• the next step 304 is for software or a user to initiate movement of the sample to a first intended laser position.
• a snapshot of the field of view of the camera/microscope is taken 305 corresponding to the current position of the sample relative to the camera.
• An embodiment of this step is illustrated in Fig. 4b showing the kernel image 403, represented by a dotted outline of crystal grain, corresponding to the intended laser position and a current image 404 of the current field of view of the camera/microscope.
• the kernel image 403 is not aligned with the current image 404, represented by a full line outline of the same crystal grain present in the kernel image 403, due to some positioning repeatability error.
• a comparing step 306 the difference of the intended laser location and the current laser location is determined by comparing the kernel image and the current image of the current field of view of the camera/microscope. If the different is determined to be within a window of acceptability, the correct motion scheme is complete 310 ; if the different is determined to not be within a window of acceptability, a computing step 307 is executed wherein a position error is computed and a set of corrective moves are issued to and executed by the motion control system 104 which moves the sample relative to the camera/microscope and laser. In embodiments this step is done with image recognition algorithms to calculate the difference between the kernel image and the current image of the current field of view of the
• the window of acceptability may be predefined, computed by software, or set by an operator.
• the corrective move can be a series of moves until the position error is within a window of acceptability.
• the step of taking a snapshot of the current position 305 is repeated as is the comparing step 306 in which the difference between the original position from the kernel image and a new current position are compared.
• the corrective motion scheme is complete 310 and the laser is fired at the intended laser position on the crystal grain. This causes a sample of the crystal grain to be suspending in a carrier gas and analyzed in a spectrometry instrument allowing the composition of the crystal grain to be determined for such application as zircon crystal grain dating.
• the primary advantage of this invention is to apply a corrective motion scheme to allow for extremely high precision of laser placement greatly improving the specifications of the same open-loop XYZ stage control and motion system, without adding any system level hardware additions/costs.
• a set of zircon crystal grains could include only 1 grain while in others a set could include 2 or more grains.
• a bi-directional repeatability error may appear to shift the sample relative to the laser beam 109position.
• a method for positioning a laser on a crystal grain on a sample on a support surface during a laser ablation procedure comprising: setting an ablation pattern for a sample during a scan placement process comprising; positioning the sample relative to a laser to multiple intended laser positions on the sample with a motion control system, saving position coordinates for each intended laser position, and saving a kernel image for at least one said intended laser positions; and initiating an experiment comprising; positioning the laser relative to the sample to a current position based on the saved coordinates of a chosen one of the intended laser positions with a saved kernel image, comparing a current image of the current position with the saved kernel image for the intended laser, determining a position error based on the comparison, if the position error is not within a window of acceptability, then applying an offset movement of the laser relative to the sample with the motion control system based on the position error to correct for the position error and repeat the comparing and determining steps, and if the position error is within the window of acceptability, then fire a laser beam upon the intended
• step of saving a kernel image for at least one said intended laser positions further includes saving at least one of lighting levels, zoom levels, or camera properties used when capturing the kernel image.

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• Computer Vision & Pattern Recognition (AREA)
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• Manufacturing & Machinery (AREA)
• Automation & Control Theory (AREA)
• Human Computer Interaction (AREA)
• Laser Beam Processing (AREA)
• Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
• Image Analysis (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Investigating, Analyzing Materials By Fluorescence Or Luminescence (AREA)
• Sampling And Sample Adjustment (AREA)

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• 2014
  • 2014-03-14 WO PCT/US2014/028241 patent/WO2014144012A1/en not_active Ceased
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  • 2014-03-14 JP JP2016502744A patent/JP6290371B2/ja active Active
  • 2014-03-14 CN CN201480015608.XA patent/CN105229446B/zh active Active
  • 2014-03-14 KR KR1020207031514A patent/KR102294198B1/ko active Active
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• 2018
  • 2018-02-07 JP JP2018020149A patent/JP6463526B2/ja active Active

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