Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
  • G01F25/0092—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume for metering by volume
• • 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—Program-control systems
  • G05B19/02—Program-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 program data in numerical form
  • G05B19/401—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 program data in numerical form characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes
• • 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—Program-control systems
  • G05B19/02—Program-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 program data in numerical form
  • G05B19/401—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 program data in numerical form characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes
  • G05B19/4015—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 program data in numerical form characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes going to a reference at the beginning of machine cycle, e.g. for calibration
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P74/00—Testing or measuring during manufacture or treatment of wafers, substrates or devices
  • H10P74/23—Testing or measuring during manufacture or treatment of wafers, substrates or devices characterised by multiple measurements, corrections, marking or sorting processes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C25/00—Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D18/00—Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D18/00—Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
  • G01D18/001—Calibrating encoders
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/18—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration in two or more dimensions
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P21/00—Testing or calibrating of apparatus or devices covered by the preceding groups
• • 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
  • G05B2219/39—Robotics, robotics to robotics hand
  • G05B2219/39026—Calibration of manipulator while tool is mounted
• • 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
  • G05B2219/45—Nc applications
  • G05B2219/45235—Dispensing adhesive, solder paste, for pcb
• • 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
  • G05B2219/45—Nc applications
  • G05B2219/45238—Tape, fiber, glue, material dispensing in layers, beads, filling, sealing
• • 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
  • G05B2219/50033—Align tool, tip with a calibration mask
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K2203/00—Indexing scheme relating to apparatus or processes for manufacturing printed circuits covered by H05K3/00
  • H05K2203/01—Tools for processing; Objects used during processing
  • H05K2203/0104—Tools for processing; Objects used during processing for patterning or coating
  • H05K2203/0126—Dispenser, e.g. for solder paste, for supplying conductive paste for screen printing or for filling holes
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/30—Assembling printed circuits with electric components, e.g. with resistors
  • H05K3/32—Assembling printed circuits with electric components, e.g. with resistors electrically connecting electric components or wires to printed circuits
  • H05K3/34—Assembling printed circuits with electric components, e.g. with resistors electrically connecting electric components or wires to printed circuits by soldering
  • H05K3/3465—Application of solder
  • H05K3/3478—Application of solder preforms; Transferring prefabricated solder patterns

Definitions

• the present invention relates generally to methods for calibrating a viscous fluid dispensing system. More particularly, the invention relates to methods for calibrating the placement of viscous fluids dispensed by a viscous fluid dispensing system.
• PCB printed circuit boards
• viscous fluids include, by way of example, general purpose adhesives, solder paste, solder flux, solder mask, grease, oil, encapsulants, potting compounds, epoxies, die attach pastes, silicones, RTV and cyanoacrylates.
• a PCB is often delivered to a viscous fluid dispenser that is mounted to a gantry system and thus movable with three axes of motion above the PCB, for example in a standard X-Y-Z Cartesian coordinate system.
• the moving fluid dispenser operates in combination with a camera, also mounted to the gantry system and fixed relative to the fluid dispenser, and is capable of dispensing dots of viscous fluid at desired locations on the PCB.
• placement accuracy As PCB's are becoming denser and the components mounted thereon are becoming smaller, it is increasingly critical that the dots of viscous fluid are dispensed with a high degree of accuracy, referred to generally as "placement accuracy” or “positional accuracy.”
• placement accuracy is by comparing the location at which a dot was intended to be dispensed with the location at which the dot was actually dispensed.
• placement accuracy is by comparing the location at which a dot was intended to be dispensed with the location at which the dot was actually dispensed.
• Many factors contribute to poor placement accuracy of dispensed dots of viscous fluid, including poor camera calibration, misalignment or slight shifting of physical components in the fluid dispensing system, internal software errors, and human error associated with data entered into the software programs controlling the fluid dispenser or camera systems.
• a critical step in operating a fluid dispensing system is calculating a camera-to-needle offset value to account for the difference in positions of the fluid dispenser and the camera operating therewith relative to the X-Y plane along which the fluid dispenser and camera move.
• Camera-to-needle offset refers to the distance between the center of the fluid dispenser nozzle, or needle, from which fluid is dispensed and the center of the camera image sensor used to identify the locations at which fluid is dispensed. This camera- to-needle offset value is accounted for by the computer operating the fluid dispensing system so that fluid is then properly dispensed at locations identified by the camera in view of its offset from the dispensing nozzle.
• a fluid dispensing nozzle and a camera image sensor may be mounted to the gantry system such that their centers are separated by a distance of fifteen centimeters. This fifteen centimeters is recorded as the camera-to-needle offset value, which is then accounted for by the fluid dispensing system when calculating the locations at which to dispense dots of fluid after the locations have been identified by the camera.
• An exemplary method for calibrating a fluid dispensing system includes the steps of locating an external reference point with an optical sensor, moving a fluid dispenser to the external reference point, dispensing fluid with the fluid dispenser at the external reference point, locating the dispensed fluid with the optical sensor, calculating a distance between the location of the external reference point and the location of the dispensed fluid, determining a correction value based at least in part on the calculated distance, and using the correction value to improve placement accuracy of dispensed fluid.
• FIG. 1 is a schematic view of a computer-controlled viscous fluid dispensing system including a fluid dispenser and a video camera positioned above a platform.
• FIG. 2 is a top view of a fiducial tile having a plurality of fiducials printed thereon.
• FIG. 3 is a flowchart showing simplified steps of a dot placement calibration routine according to an embodiment of the invention.
• FIG. 4 is a detailed flowchart similar to that of FIG. 3, but showing detailed steps of the dot placement calibration routine.
• FIG. 5A is a top view similar to FIG. 2, but showing details of a path traversed by the camera for locating fiducials disposed on the fiducial tile according to an embodiment of the invention.
• FIG. 5B is a top view similar to FIG. 2, but showing details of a path traversed by the fluid dispenser for dispensing starter dots of viscous fluid according to an embodiment of the invention.
• FIG. 5C is a top view similar to FIG. 2, but showing details of a path traversed by the fluid dispenser for dispensing calibration dots of viscous fluid at the center of each fiducial, according to an embodiment of the invention.
• FIGS. 6A-6G are views of a graphical user interface showing various stages of user interaction with a dot placement calibration routine, according to an embodiment of the invention.
• FIG. 1 is a schematic representation of a computer-controlled viscous fluid dispensing system 10 of the type
• the system 10 includes a fluid dispenser 12 and a video camera 14 attached to an X-Y positioner (not shown) that is positioned above a platform 16.
• the fluid dispenser 12 is mounted on a Z-axis drive (not shown) that is suspended from the X-Y positioner, such that the fluid dispenser 12 may translate vertically relative to platform 16 below for dispensing dots of viscous fluids on a substrate positioned on the platform 16.
• the X-Y positioner and Z-axis drive provide three substantially perpendicular axes of motion for the fluid dispenser 12.
• the fluid dispensing system 10 includes a computer 1 1 for providing the overall control for the system 10.
• the computer 1 1 may be a programmable logic controller ("PLC") or other microprocessor based controller, a personal computer, or other conventional control devices capable of carrying out the functions described herein as will be understood by those of ordinary skill in the art.
• the computer 1 1 may include a processor, a memory, a mass storage memory device, an input/output (I/O) interface, and a Human Machine Interface (“HMI”) such as a Graphical User Interface (“GUI").
• HMI Human Machine Interface
• the computer 1 1 may also be operatively coupled to one or more external resources via a network or the I/O interface.
• External resources may include, but are not limited to, servers, databases, mass storage devices, peripheral devices, cloud-based network services, or any other suitable computer resource that may used by the computer 1 1 .
• Substrates such as PCB's (not shown), which are to have dots of viscous fluid, such as adhesive, epoxy, solder, etc, dispensed thereon by the fluid dispenser 12, are manually loaded or horizontally transported to a position directly beneath the fluid dispenser 12 by an automatic conveyor (not shown).
• the video camera 14 identifies the locations on the substrate or other target disposed on the platform 16 at which a dot of viscous fluid is to be dispensed.
• the computer 1 1 controls the X-Y positioner to move the fluid dispenser 12 to a position above the desired location above the substrate or other target, and further controls the Z-axis drive to position the fluid dispenser 12 at the proper height for
• the platform 16 includes a calibration station 20 configured to accommodate an external target tile 22, referred to as a fiducial tile, that may be removably placed on the platform 16 and is used for calibrating the fluid dispensing system 10.
• the fiducial tile 22 is planar and has a generally square shape.
• the fiducial tile 22 includes at least one, and preferably at least eight, external reference points 24 printed thereon, referred to as "fiducials" or “targets.”
• the eight fiducials 24 are circular in shape, equally sized at 2mm in diameter, and equally spaced on the tile 22 in a square or box-like pattern, such that any one side of the square or box-like pattern includes three fiducials 24 positioned with equidistant spacing.
• the target tile 22 may additionally include a centrally positioned fiducial 24c, such that tile 22 includes a total of nine fiducials arranged in a 3-by-3 grid pattern.
• the central fiducial 24c may be used as an alternative to one of the outer fiducials 24 during initial setup of the calibration routine 29 described below, and is not necessary for actual performance of the calibration routine 29. Persons of ordinary skill in the art may adapt the calibration methods disclosed herein to fiducial tiles and fiducials of any shape, size, quantity, and spacing desired.
• FIG. 3 illustrates a simplified version of an automated dot placement calibration routine 29, used for calibrating the placement of dots dispensed by a viscous fluid dispensing system 10, according to one embodiment of the invention.
• the computer 1 1 first, at 30, accesses a stored preliminary camera-to-needle offset value.
• the camera-to-needle offset is a two-element array representing the distance, in an X-Y coordinate system, between the center of the nozzle of fluid dispenser 12 and the center of the imaging sensor (not shown) of the video camera 14.
• the fluid dispenser 12 and video camera 14 are each mounted to the X-Y positioner so as to ideally maintain a known distance between one another in the X-Y plane.
• the fluid dispenser 12 and the camera 14 may be fixed relative to one another in the X-Y plane.
• the fluid dispenser 12 may be movable relative to the camera 14 in the X-Y plane such that the distance defined between the dispenser 12 and the image sensor of the camera 14 is deliberate, measurable, and repeatable.
• the camera-to-needle offset value i.e., the X-Y distances between the fluid dispenser 12 and image sensor of the video camera 14, must be accounted for by the computer 1 1 so that the dispenser 12 may accurately dispense fluids at locations identified by the camera 14.
• the preliminary camera-to-needle offset value stored within the computer 1 1 may be, for example, the camera-to-needle offset value from a previous calibration cycle, or it may be a value taught to the computer 1 1 by a user after taking proper measurements.
• the measurements for the preliminary offset value may, for example, be taken using computer aided design ("CAD") software.
• CAD computer aided design
• the computer 1 1 commands the camera 14 to move and locate each fiducial 24 on the fiducial tile 22.
• the camera 14 and fluid dispenser 12 both approach each fiducial from a different direction in the X-Y plane so as to account for error associated with each of eight different directions of approach.
• the computer 1 1 commands the fluid dispenser 12 to move to the center of each of the eight outer fiducials 24 and dispense a dot of viscous fluid thereon.
• the term "center” refers to the geometric center in the X-Y plane, known as a centroid, of the object referenced.
• a fiducial 24, a dot dispensed thereon, the nozzle of the fluid dispenser, and the lens of the camera 14 each have a geometric center (centroid) in the X-Y plane, which is used for calculating X-Y distances between any two of these objects.
• the centroid of a geometric shape is easily determined, and for a dispensed dot having an irregular, non-geometric shape, its centroid may be calculated by a person of ordinary skill in the art.
• the computer 1 1 then commands the camera 14 to locate each of the eight dots dispensed on the fiducial tile 22.
• the computer 1 1 compares the location of each fiducial 24 to the location at which the corresponding dot of fluid was actually dispensed. Specifically, for each fiducial 24, the computer 1 1 determines the difference between the X-Y coordinates of the center of the fiducial 24 and the X-Y coordinates of the center of its corresponding dispensed dot. The computer 1 1 then determines the average of these eight values and stores the averaged value, referred to as the "dot offset error value.”
• the computer 1 1 compares the dot offset error value to a limit value that is taught or otherwise known by the computer 1 1 . If the dot offset error value is less than the limit value, then the fluid dispensing system 10 is deemed to be operating with sufficient dot placement accuracy such that it is adequately calibrated, and the calibration routine ends. If the dot offset error value is not less than the limit value, the computer 1 1 recognizes that the system 10 is not operating with sufficient dot placement accuracy. Thus, the calibration routine 29 does not end. Instead, the computer 1 1 , at 36, recalculates or otherwise adjusts the camera-to-needle offset value to account for additional error within the system 10.
• the computer 1 1 then repeats the process described above, starting at 31 , in order to improve dot placement accuracy.
• the camera-to-needle offset adjustment is described in greater detail below with reference to FIG. 4. Accordingly, the process described herein is an iterative process, in that the computer 1 1 repeats steps 31 -36 until the dot placement error value is less than the limit value, such that dot placement accuracy has been sufficiently improved.
• the automated dot placement calibration routine 29 of FIG. 3 is shown with additional detail, as routine 39.
• the computer 1 1 first sets a preliminary camera-to-needle offset array C2N, as described above with reference to FIG. 3.
• the computer 1 1 instructs a user to find the locations of the upper-left fiducial 24a and the lower-right fiducial 24b, and then teach these locations to the computer 1 1.
• the computer 1 1 is programmed to understand that the fiducial tile 22 includes eight circular, outer fiducials 24 spaced equidistantly in a square pattern.
• the computer 1 1 may then determine anticipated locations of the remaining fiducials 24.
• the computer 1 1 may be programmed to understand alternative patterns and quantities of fiducials as well.
• the computer 1 1 then commands the camera 14 to locate all eight fiducials 24 based on their anticipated locations.
• the camera 14 approaches the anticipated location of each fiducial 24 from a different direction, as described above. Specifically, as shown by the illustrative embodiment in FIG. 5A, the camera 14 approaches from each of the four Cardinal directions and their four combinations.
• Cardinal directions refers to the north, east, south, and west directions in an X-Y plane, denoted N, E, S, and W, respectively, in FIG. 5A.
• the camera 14 starts at a location near the center of the fiducial tile 22 and approaches a first fiducial 24 from the southwest direction, a second fiducial 24 from the east direction, a third fiducial 24 from the southeast direction, a fourth fiducial 24 from the north direction, a fifth fiducial 24 from the northeast direction, a sixth fiducial 24 from the west direction, a seventh fiducial 24 from the northwest direction, and an eighth fiducial 24 from the south direction.
• an encoder (not shown) is used to note the X-Y coordinates of the center of the fiducial 24.
• the X-Y coordinates of all eight fiducials 24 are then stored by the computer 1 1 in a "substrate fiducial location" array V sf .
• Persons of ordinary skill in the art may adapt the calibration methods disclosed herein such that the directions of approach include any desired directions and combinations thereof, and such that the directions of approach account for any desired number of fiducials.
• the resultant path traversed by the camera 14 defines a curvilinear shape having four arcuate legs L spaced equally in substantially ninety degree increments about the center of the fiducial tile 22.
• Approaching the eight fiducials 24 from each of the Cardinal directions and their combinations is advantageous because the fluid dispensing system 10 exhibits a different magnitude of error due to movement depending on the direction of travel, referred to as "directional error.”
• the influence of directional error on the locating of fiducials 24 or dispensed dots is thus minimized by approaching the fiducials 24 and dispensed dots from a plurality of possible directions of travel of the fluid dispenser 12 and the video camera 14 in the X-Y plane.
• the computer 1 1 commands the fluid dispenser 12 to dispense a series of starter dots 26 of fluid onto the fiducial tile 22, the starter dots 26 being of a size, shape, quantity, and pattern defined by a user.
• the starter dots 26 are dispensed with equidistant spacing to form a square-shaped pattern near the center of the fiducial tile 22, such that the starter dots 26 do not overlap any of the fiducials 24, as shown in FIG. 5B.
• the fluid dispenser 12 When dispensing the four starter dots 26, the fluid dispenser 12 approaches the locations for the first and second starter dots 26 from the northwest direction and then approaches the locations for the third and fourth starter dots 26 from the southwest directions, so as to traverse a path defining a curvilinear shape having a single arcuate leg L. Dispensing a series of starter dots 26 allows the fluid dispenser 12 to "spool-up” or “warm- up”, such that the fluid dispenser 12 is capable of dispensing accurate and precise volumes of fluid for dots dispensed thereafter.
• the computer 1 1 commands the fluid dispenser 12 to dispense a calibration dot 28 of viscous fluid at the center of each of the eight fiducials 24.
• the fluid dispenser 12 traverses the same path as that previously traversed by the camera 14 when locating each of the eight fiducials 24, described above.
• the encoder is used to note the X-Y coordinates of the location to which the fluid dispenser 12 was moved for dispensing the calibration dot 28.
• the X-Y coordinates of the dispensing location for all eight dispensed calibration dots 28 are then stored by the computer 1 1 in a "move-to- when-dispensing" array V mt .
• the computer 1 1 then commands the camera 14 to locate each of the eight dispensed calibration dots 28. As shown in FIG. 5C, the camera 14 traverses the same path as that previously traversed by the fluid dispenser 12, at 44, and by the camera 14, at 42. As the camera 14 locates each dispensed calibration dot 28, the encoder is used to note the X-Y coordinates of the center of the calibration dot 28. The X-Y coordinates of each dispensed calibration dot 28 are then stored by the computer 1 1 in a "calibration dot found" array V CC
• the computer 1 1 determines a "dot offset error" by comparing, for each dispensed calibration dot 28, the location of the center of the dispensed calibration dot 28 to the location of the center of its
• the computer 1 1 calculates and stores a dot offset error array Vdoe by taking the difference between the substrate fiducial location array V S f and the calibration dot found array V C d, denoted by:
• Vdoe V s f - Vcd
• the computer 1 1 determines a "dot offset direction" array Vdod by finding, for each dispensed calibration dot 28, the direction in which its center is offset relative to the center of its corresponding fiducial 24.
• the computer 1 1 determines an "average dot offset magnitude" value by calculating the average of the individual values stored within the dot offset magnitude array Vdom- The computer 1 1 then determines whether this average dot offset magnitude value is less than an acceptable threshold or limit value that is taught or otherwise known by the computer 1 1 .
• the acceptable limit may be defined by a user and communicated to the computer 1 1 . As discussed above with respect to FIG. 3, if the average dot offset error value is less than the acceptable limit, then the calibration routine 39 is finished.
• routine 39 continues with steps directed to recalculating or adjusting the camera-to-needle offset value so as to address sources of error not accounted for by the preliminary camera-to-needle offset value, and ultimately improve dot placement accuracy.
• the computer 1 1 determines a local camera-to-needle offset value for each dispensed calibration dot 28 by comparing the location to which the fluid dispenser 12 was moved for dispensing the calibration dot 28, to the location at which the dispensed dot 28 was actually found by the camera 14. Specifically, the computer 1 1 calculates and stores a "local camera-to-needle offset" array V
• the computer 1 1 calculates a new camera-to-needle offset value by first calculating, for each dispensed calibration dot 28, an adjusted camera-to-needle offset value that accounts for both the local camera-to-needle offset value and the commanded vs. actual error value associated with a given dispensed calibration dot 28. Specifically, the computer 1 1 calculates and stores an "adjusted camera-to-needle offset" array V C 2n by calculating the sum of the local camera-to-needle offset array V
• the computer 1 1 calculates the new camera-to-needle offset array C2N by calculating an average of the individual values stored within the adjusted camera-to-needle offset array V C 2n, denoted by:
• the new, adjusted camera-to-needle offset thus accounts for sources of error in the fluid dispensing system 10 not accounted for by the preliminary camera-to- needle offset. Accordingly, this new camera-to-needle offset may be applied to the system 10 to reduce dot offset error and thereby improve dot placement accuracy during a subsequent cycle of dot dispensing.
• the computer 1 1 prompts a user to clean the fiducial tile 22 so that an additional iteration of the calibration routine 39 may be performed.
• the computer 1 1 determines whether the calibration routine 39 has performed a number of iterations that exceeds a user-defined escape value. If the number of iterations performed does not exceed the escape value, an additional iteration of the routine 39 is performed starting at 42. If the number of iterations performed exceeds the escape value, the computer 1 1 proceeds to 55, at which the computer 1 1 prompts the user to indicate whether additional iterations of the routine 39 are desired. If additional iterations are not desired, the calibration routine 39 is finished and no additional iterations are performed. If an additional iteration is desired, the computer 1 1 returns to 42 for an additional iteration of the routine 39.
• GUI graphical user interface
• the GUI 59 has a view finder 60 on which the computer 1 1 displays fiducials 24 and dispensed dots 28 identified by the camera 14.
• FIGS. 6A-6G show a series of screen shots taken from the computer 1 1 , which may be a personal computer for example, illustrating various stages of user interaction with GUI 59.
• a user initiates the calibration routine 39 by selecting the routine 39 in the RUN > SETUP screen of the computer 1 1 , for example.
• the GUI 59 displays on the computer 1 1 , and the user is first directed to a "Main" tab 61.
• the user then moves the camera 14 to a desired location in the X-Y plane at which the fluid dispensing system 10 will measure a height, in the Z-direction, of the fluid dispenser 12 nozzle relative to the fiducial tile 22 before dispensing a dot 28 thereon.
• This X-Y location is referred to as the "height-sense location,” and is accounted for by the computer 1 1 when commanding the fluid dispenser 12 to move toward a lowered position along the Z-axis for dispensing a dot 28 on the fiducial tile 22.
• This height may be measured using any suitable device (not shown), such as a laser or a mechanical measuring device, for example.
• the user selects "Teach HS Location” 62 to teach the height-sense location to the computer 1 1 operating the calibration routine 39.
• the user selects "For Fiducials" 64 to set the parameters that the routine 39 will use to find the fiducials 24.
• the user selects a "Dot Finder" tab 70 and defines a Search Window 72, a Camera Settling Time 74, and an
• a Dark/Light Threshold 82 defines the shade of grey corresponding to the edges of a circle, such as a fiducial 24 or a dispensed dot 28, identified by the camera 14.
• a Dark/Light Threshold 82 value of zero corresponds to black, and a value of 255 corresponds to white. Accordingly, if a fiducial 24 is identified by the camera 14 as a white circle, a value of approximately 200 should be entered. If the fiducial 24 is identified as a black circle, then a value of approximately 80 should be entered.
• Restrict Min Diameter 84 and Restrict Max Diameter 86 restrict the minimum and maximum diameter of a circle identifiable by the camera 14 operated by the routine 39. These parameters 84, 86 are used to filter out "bad" circles when multiple circles are identified by the camera 14 and displayed within the view finder 60.
• the values entered for these parameters 84, 86 control the widths of an outer box 87 and an inner box 88 drawn by the computer 1 1 within the view finder 60.
• the width of the outer box 87 corresponds to the value entered for Restrict Max Diameter 86
• the width of the inner box 88 corresponds to the value entered for Restrict Max Min Diameter 84.
• the units associated with the values entered for these parameters 84, 86 are pixels.
• Roundness 89 corresponds to the anticipated roundness of a circle, such as a fiducial 24 or a calibration dot 28, to be identified by the camera 14.
• a perfect circle corresponds to a Roundness 88 value of 100%
• an amorphous blob corresponds to a Roundness 88 value of 0%.
• Circumference Points 90 corresponds to how much of an identified circle, such as a fiducial 24 or a dispensed dot 28, will be visible. For example, a full circle corresponds to a value of 100%, and a half-circle corresponds to a value of 50%. If the user anticipates that full circles will be consistently identified, a value of approximately 90% should be entered.
• the user selects a "Test” tab 98 while a fiducial 24 is shown in the view finder 60 to determine whether the routine 39 is able to properly identify the fiducial 24.
• a "Test” button 100 is preferably selected multiple times for the same fiducial 24, and additionally for at least one other fiducial 24 to simulate multiple runs. If selecting the "Test” button 100 highlights erroneous circles, the user should then return to the previous tabs 66, 70, and 80 to adjust the proper parameters, and then return to the "Test" tab 98 to ensure proper operation. Once the tests are satisfactory, the user then selects "Save Light Levels" 101 to save the settings used to identify the fiducials 24.
• the user selects "For Dots” 1 10 to begin setting the parameters used to identify the dispensed dots 28 during the routine 39.
• the user positions the center of a fiducial 24 within the view finder 60 and selects "Dispense dot at current location” 1 12. This commands the fluid dispenser 12 to dispense a single dot 28 than can be used to set the Dot Finder 70 parameters.
• the user then repeats the steps described above using the dispensed dot 28, rather than a fiducial 24, as the target. Once the dispensed dot settings are set and saved, the user then selects the "Next" button 1 14.
• the routine 39 then prompts the user to locate a first, upper-left fiducial 24a.
• the user selects "Next" 1 14 to continue.
• the user positions the upper-left fiducial 24a in the view finder 60 and selects "Teach” 1 16, which causes the computer 1 1 to save the X-Y coordinates of the upper-left fiducial 24a.
• the routine 39 then prompts the user to locate a second, lower-right fiducial 24b.
• the user selects "Next" 1 14 to continue.
• the user positions the lower-right fiducial 24b in the view finder 60 and selects "Teach” 1 16, which causes the computer 1 1 to save the X-Y coordinates of the lower-right fiducial 24b.
• the routine 39 locates all eight fiducials 24, dispenses a calibration dot 28 at the center of each fiducial 24, locates the dispensed calibration dots 28, and calculates a dot offset error.
• a pop-up error window alerts the user, by displaying a message such as "The average dot offset magnitude of [value] exceeds the acceptable threshold of [value] inch.”
• the user acknowledges the message by selecting an "OK" button (not shown), wipes the fiducial tile 22 clean, and then selects "Next" 1 14.
• the routine 39 may then repeat the steps described above in order to improve dot placement accuracy of a fluid dispensing system. If the new dot offset error is less than the user-defined limit, the routine 39 is successful and a pop-up window (not shown) displaying the results will appear.
• the calibration routine 39 and GUI 59 described above may be modified as needed by persons of ordinary skill in the art for use with fiducial tiles having fiducials of any suitable shape, quantity, and configuration.

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• 2014
  • 2014-12-04 US US14/560,032 patent/US10082417B2/en active Active
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