Camera calibration for robotic arrayed inkjet printing

Abstract

To provide a method of calibrating a camera for use with robotic inkjet printing.SOLUTION: The present application is directed to uses with a printhead assembly that is attached to a robot. One application provides a system for inkjet printing on large objects such as commercial aircraft surfaces. The application provides calibrating a camera with relation to the motion of the robot. The calibration is achieved using one or more calibration artifacts printed by the inkjet system.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] This disclosure relates generally to the field of inkjet printing, and more particularly to camera calibration for use in detecting errors in inkjet printing. [Background technology]

[0002]

[0002] Inkjet printing devices can be configured to print on large surfaces. Printing contexts include, but are not limited to, printing on various aircraft parts, such as fuselages, wings, and flight control components of commercial aircraft. Other contexts include, but are not limited to, printing on large equipment parts (e.g., frames, work beds) and industrial machinery.

[0003]

[0003] An inkjet printing device includes an inkjet printhead assembly that is attached to a robot. In one example, the printhead assembly includes a printhead housing having several individual printheads. Each inkjet printhead ejects a different color of ink, such as cyan, yellow, magenta, and black. The printheads are controlled as the robot moves the printhead assembly across a surface during printing.

[0004]

[0004] A problem with large scale inkjet printing is the need for a large robot sized to extend over a portion or the entire surface to be printed. The printhead assembly is mounted at one end of the robot and is subject to high dynamic loads as a result of its size. Inkjet printing has a very small margin of error in ink application before visible defects occur. A camera is used to monitor the inkjet printing and detect visible errors. The camera should be calibrated to provide localized, low latency visual monitoring to minimize visible printing defects. The camera should be configured to identify various errors in inkjet printing, such as, but not limited to, nozzle stalls between overlapping passes of ink application and errors in the motion system. Summary of the Invention

[0005] One aspect is directed to a method of calibrating a camera for use with robotic inkjet printing, the method including printing a calibration artifact including one or more control points, the calibration artifact being printed with a printhead assembly coupled to a robot, the calibration artifact being printed at a known location on an object, printing the calibration artifact, using the robot to move a camera coupled to the printhead assembly to capture image data for the calibration artifact, detecting the calibration artifact from the image data, determining the detected location of the calibration artifact based on a position of the robot when the image data was captured, and calibrating the camera based on the known location of the calibration artifact and the detected location of the calibration artifact.

[0006]

[0006] In another aspect, the calibration artifact includes one or more control points positioned at known control point locations, and the method further includes identifying detected locations of the control points from image data captured by the camera, and calibrating the camera based on the known control point locations of the calibration artifact and the detected locations of the control points of the calibration artifact.

[0007]

[0007] In another aspect, the method further includes generating a scan path for the robot to move the print head assembly over the object, and capturing image data of the calibration artifact while the robot moves the print head assembly along the scan path.

[0008]

[0008] In another aspect, the method further includes capturing a three-dimensional scan of the surface of the object using a metrology system prior to printing the calibration artifacts in the known locations.

[0009]

[0009] In another aspect, the method further includes determining movement of the robot within a measurement coordinate system based on a three-dimensional scan of the object.

[0010]

[0010] In another aspect, the method further includes determining a position of the robot based on a tool center point of the printhead assembly.

[0011]

[0011] In another aspect, the method further includes calibrating the camera based on a known distance on the print head assembly between the tool center point and the camera.

[0012]

[0012] In another aspect, the calibration artifact is a first calibration artifact, and the method further includes printing a further calibration artifact at a known location on the object, capturing further image data of the further calibration artifact, and calibrating a camera relative to the robot based on a difference between the known location of the calibration artifact and the tool center point at the time the image data of the calibration artifact was captured.

[0013]

[0013] In another aspect, capturing image data of the calibration artifact includes capturing the image data using a line scan camera.

[0014]

[0014] One aspect is directed to a method of calibrating a camera for use with robotic inkjet printing, the method including determining dimensions of an object in a coordinate system based on a three-dimensional scan of the object with a metrology system, printing a calibration artifact on the object with a printhead assembly coupled to a robot, the calibration artifact being printed at a known location on the object in the coordinate system, printing the calibration artifact on the object, monitoring movement of the robot in the coordinate system while the robot moves over the object, using the robot to move a camera over the object to capture image data of the calibration artifact, determining a location of a tool center point of the printhead assembly at the time image data of the calibration artifact was captured based on a location of the robot when the image data was captured by the camera, and calibrating the camera relative to the robot based on a difference between the known location of the calibration artifact and the tool center point at the time image data of the calibration artifact was captured.

[0015] In another aspect, the method further includes calibrating the robot in a coordinate system of the metrology system prior to printing the calibration artifact on the object.

[0016] In another aspect, the method further includes designing a calibration artifact and including one or more control points in the calibration artifact.

[0017]

[0017] In another aspect, the calibration artifact is a first calibration artifact, and the method further includes printing a further calibration artifact at a known location on the object, capturing image data of the further calibration artifact, and calibrating a camera relative to the robot based on a difference between the known location of the calibration artifact and the tool center point at the time the image data of the calibration artifact was captured.

[0018] In another aspect, calibrating the camera relative to the robot includes taking into account a known distance between the tool center point and the position of the camera on the print head assembly.

[0019]

[0019] One aspect is directed to an inkjet printing system for printing on an object. The inkjet printing system includes a printhead assembly including a plurality of inkjet printheads. The printhead assembly is configured to be attached to a robot. A control unit is operatively connected to the printhead assembly and the robot for moving the printhead assembly relative to the object. The control unit includes processing circuitry. The processing circuitry is configured to: print a calibration artifact including one or more control points at a known position; operate the robot to move a camera coupled to the printhead assembly over the object to capture image data of the calibration artifact; detect the calibration artifact from the image data; identify the detected position of the calibration artifact based on a position of the robot when the image data was captured; and calibrate the camera based on the known position of the calibration artifact and the detected position of the calibration artifact.

[0020]

[0020] In another aspect, the control unit is configured to monitor a position of the printhead assembly based on a tool center point of the printhead assembly.

[0021]

[0021] In another aspect, the control unit is configured to determine the detected position of the calibration artifact based on a known distance between the camera and a tool center point of the print head assembly.

[0022] In another aspect, a metrology system determines a three-dimensional shape of an object.

[0023]

[0023] In another aspect, the control unit is configured to identify the calibration artifact based on a set of calibration artifacts stored in the memory circuit.

[0024] In another aspect, a user interface includes an input device and a display, the user interface configured to send signals to the processing circuit to control an aspect of the calibration of the camera.

[0025]

[0025] The above-described features, functions, and advantages can be realized alone in various aspects or can be combined in further multiple aspects, details of which can be confirmed by referring to the following description and the attached drawings. [Brief description of the drawings]

[0026] [Figure 1]

[0026] FIG. 1 is a perspective view of an object and a measurement system and control unit configured to measure the object and calibrate the camera. [Diagram 2]

[0027] FIG. 1 is a schematic diagram of a printhead assembly coupled to a robot for inkjet printing of objects. [Diagram 3]

[0028] FIG. 2 is a perspective view of a printhead assembly. [Figure 4A]

[0029] FIG. 2 is a schematic diagram of a calibration artifact. [Figure 4B]

[0030] FIG. 2 is a schematic diagram of a calibration artifact. [Diagram 5]

[0031] 1 is a flow chart of a method for calibrating a camera relative to a robot. [Figure 6]

[0032] 1 is a flow chart of a method for calibrating a camera relative to a robot. [Figure 7]

[0033] 1 is a flow chart of a method for calibrating a camera relative to a robot. [Figure 8]

[0034] FIG. 2 is a schematic diagram of a control unit that controls the process of camera calibration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027]

[0035] The present application provides a system for inkjet printing, particularly for printing on large objects such as the surface of a commercial aircraft, that provides for calibrating one or more cameras coupled to a printhead assembly with respect to the movement of a robotic inkjet system to which it is attached through the use of one or more calibration artifacts printed by the inkjet system.

[0028]

[0036] The application provides a methodology for the measurement of camera internal characteristics, external characteristics, and ink color recognition for a robot-mounted inkjet printhead by application and identification of one or more calibration artifacts at known locations within the coordinate frame of the overall robot motion. In some embodiments, the calibration artifact includes one or more control points printed on the object and at precisely known locations within the motion coordinate system for the target robotic inkjet system. This arrangement significantly reduces the degree of error in identifying the relationship between the external coordinate system of the camera and the robotic inkjet end effector. This calibration supports an accurate, low latency inkjet printing defect detection and correction process by identifying the position of the camera relative to the robotic inkjet system, and provides a means to locate defects identified in the line scan image and support targeted correction procedures.

[0029]

[0037] Inkjet printing systems and methods can be used to print on a variety of different objects 100. Figure 1 shows an example of an object 100 that includes a commercial aircraft. In some embodiments, printing occurs after the object is assembled, such as the assembled aircraft of Figure 1. In other embodiments, printing occurs on an object 100 that is composed of smaller parts that may (or may not) later be assembled into a larger assembly. Examples of smaller objects 100 that may be printed and then assembled using an aircraft assembly include, without limitation, vertical and horizontal stabilizers, engine housings, and portions of the fuselage.

[0030]

[0038] A metrology system 50 measures the dimensions of the object 100. The metrology system 50 includes one or more instruments for performing measurements of the object 100. In some embodiments, the metrology system 50 includes one or more laser trackers that precisely measure the object 100 by identifying one or more optical points and / or portions of artifacts on the object 100. In some embodiments, the metrology system 50 includes a coordinate measuring machine (CMM) that measures the geometric dimensions of the object 100 by sensing discrete points on a surface using a probe. In metrology systems 50 with two or more instruments, the instruments may be the same or different. In some embodiments, the metrology system 50 includes a control unit having computer processing capabilities for identifying the dimensions. Additionally or alternatively, the metrology system 50 is operatively connected to a control unit 90 that oversees a calibration process.

[0031]

[0039] The measurements of the metrology system 50 are used to define a coordinate system 99 for identifying positions on the object 100. This coordinate system 99 is used by the control unit 90 during the calibration of the camera 30, the inkjet printing of the object 100, and / or the movement of the robot 40.

[0032]

[0040] 2 shows a robot 40 configured to move inkjet printhead assembly 20 during printing of an object 100. Robot 40 includes a base 41 that supports one or more linkages 42. Base 41 may be configured to be positioned in a fixed location or may include wheels or be otherwise movable relative to object 100. Articulation joints 43 provide relative movement between linkages 42 and / or inkjet printhead assembly 20. The size, shape, and movement capabilities of robot 40 may vary depending on the needs of the print job.

[0033]

[0041] The printhead assembly 20 is mounted on one end of the robot 40. FIG. 3 shows the printhead assembly 20 in more detail. The printhead assembly 20 includes a housing 21. Inkjet printheads 22, 23, 24, 25 are mounted within the housing 21, each configured to eject a different color ink to generate a full color palette that can be used in printing. In some embodiments, the printheads include a cyan printhead 22, a yellow printhead 23, a magenta printhead 24, and a black printhead 25. This is a typical printhead arrangement. In that case, the printhead assembly 20 passes over the object 100 in a normal printing direction, with the cyan printhead 22 as the leading edge, followed by the yellow printhead 23, the magenta printhead 24, and the black printhead 25 as the trailing edge, ejecting ink in a color sequence to generate the colors of the pattern in a manner known in the art. Depending on a particular implementation of the printhead assembly 20 according to the present disclosure, alternative color sequences and / or alternative base colors may be used. The printhead assembly 20 includes a tool center point (TCP) 26. The TCP 26 serves as an origin used to locate the printhead assembly 20 within a coordinate system 99.

[0034]

[0042] During printing, the robot 40 moves the printhead assembly 20 in various ways, including along one or more axes. One type of movement is along a first axis (e.g., X-axis) corresponding to side-to-side movement of the housing 21 in the printing direction. The positive X-direction is the direction in which the printheads 22, 23, 24, 25 move in a line, with the cyan printhead 22 passing over the object first. The second axis (e.g., Y-axis) is the up-down direction of movement of the printhead assembly 20. The third axis (e.g., Z-axis) represents movement of the printhead assembly 20 towards and away from the object 100 perpendicular to the surface of the object 100 being printed. The robot 40 can also rotate the printhead assembly 20 in various ways with various rotational degrees of freedom, including roll, pitch, and yaw.

[0035]

[0043] One or more cameras 30 are attached to the printhead assembly 20 to capture images from the object 100. Various types of cameras 30 can be used to capture image data. In some embodiments, the camera 30 includes a single sensor element configured to generate a two-dimensional image. One embodiment is a line scan camera 30 that captures a row of pixels at a time as the printhead assembly 20 passes over the object 100. The line scan camera 30 is positioned on the printhead assembly 20 at a known position relative to the TCP 26. This position is used during calibration of the camera 30, as will be described in more detail below. FIG. 3 includes an embodiment having a single camera 30 coupled to the printhead assembly 20. In other embodiments, two or more cameras 30 are coupled to the printhead assembly 20. In these embodiments, the cameras 30 may be the same or different.

[0036]

[0044] The control unit 90 controls the robot 40 to move the printhead assembly 20 along various directions and rotations to print on the object 100. In some embodiments, the control unit 90 uses a location on the printhead assembly 20 to monitor the movement. In one embodiment, the control unit 90 uses the TCP 26, which provides a base reference point when determining the position. In other embodiments, the control unit 90 tracks different points when monitoring the position of the printhead assembly 20. In various embodiments, the location used to monitor the movement of the printhead assembly 20 is located at a known location from the camera 30. The known location is a known distance from the camera 30.

[0037]

[0045] During the inkjet printing process, the control unit 90 monitors the object 100 for visible printing defects. To provide accurate monitoring, the camera 30 is calibrated to the movements of the robot 40. The calibration process uses one or more calibration artifacts 60 that are printed on the object 100 by the printhead assembly 20. The calibration artifacts 60 are located at known positions in the coordinate system 99. After printing, the robot 40 moves the camera 30 over the object to detect the one or more artifacts 60. The one or more positions detected based on the captured image data are compared to the one or more known positions to calibrate the camera 30.

[0038]

[0046] Calibration artifacts 60 are configured to be printed on object 100 by print head assembly 20. The number of calibration artifacts 60 used during calibration can vary from a single calibration artifact 60 to multiple calibration artifacts 60. When multiple calibration artifacts 60 are used, the calibration artifacts 60 may be the same or different.

[0039]

[0047] The calibration artifact 60 includes one or more control points 61. The control points 61 are specific identifiable points on the calibration artifact 60 that can be detected during analysis of image data captured by the camera 30. The calibration artifact 60 with the control points 61 can be varied depending on the test and can range from a robust pixel offset to a minor pixel offset. FIG. 4A is an example of a calibration artifact 60 including a rectangular box. The control points 61 are located at one or more of a corner and a center point. FIG. 4B shows another calibration artifact 60 including a pair of straight lines. The control points 61 are located at the intersections of the lines. The calibration artifact 60 can be printed in a variety of colors within the color gamut of the print heads 22, 23, 24, 25. The calibration artifact 60 is for calibrating one or more of alignment and color recognition.

[0040]

[0048] The method may be implemented using any number of different forms of calibration artifact 60. In some embodiments, the calibration incorporates ink gamut factors into the calibration of perceived ink color.

[0041]

[0049] 5 shows a method for calibrating the camera 30 relative to the robot 40 used to move the print head assembly 20. A metrology system 50 measures the object 100 and defines a coordinate system 99 (block 200). In some embodiments, this involves collecting a 3D scan of the surface of the object 100 using the metrology system 50 having one or more metrology devices.

[0042]

[0050] One or more calibration artifacts 60 are printed on the object 100 using the printhead assembly 20 (block 202). In some embodiments, this includes using the robot 40 to move the printhead assembly 20 over the object 100. The printhead assembly 20 prints the one or more calibration artifacts 60 at known locations on the object 100. In some embodiments, after the calibration artifacts 60 are printed on the object 100, their locations are identified by the metrology system 50. The one or more metrology devices scan the object 100 and detect their locations on the object 100. In some embodiments, the calibration artifacts 60 are printed at specific identifiable points on the object 100. Examples include, but are not limited to, the intersection of a wing and fuselage of an aircraft, or the tips of the wings.

[0043]

[0051] After the calibration artifact 60 is printed on the object 100, a scan path is developed (block 204) that will move the print head assembly 20 along the object 100 and over the calibration artifact 60. The scan path enables the robot 40 to move the camera 30 over the calibration artifact 60 so that the calibration artifact 60 can be captured by the camera 30. The number and configuration of scan paths can vary, provided that the camera 30 is capable of capturing the calibration artifact 60 while moving.

[0044]

[0052] After the calibration artifact 60 is printed and the scan path is defined, the robot 40 moves the printhead assembly 20 along the scan path (block 206). The robot 40 moves the printhead assembly 20 over the object 100 at various poses and depths with minimal angular deflection along each trajectory. During the movement, the control unit 90 monitors the movement of the robot 40 and the position of the printhead assembly 20. The position information is referenced in a coordinate system 99 defined by the metrology system 50. In some embodiments, the position of the printhead assembly 20 is based on the TCP 26. In addition to the position, the control unit 90 monitors the timing of the movement of the robot 40 and the printhead assembly 20. Thus, the control unit 90 monitors the position and time that the printhead assembly 20 moves over various locations on the object 100, including over the calibration artifact 60.

[0045]

[0053] The camera 30 captures image data including the calibration artifacts 60 as the print head assembly 20 moves over the object 100. In some embodiments, the camera 30 continuously captures image data of the object 100. In some embodiments, the camera 30 captures the image data periodically, such as recording image data at various frequencies, as the camera 30 is moved across the object 100. The corresponding time that the image data was captured is also associated with the image data.

[0046]

[0054] The control unit 90 receives the image data and identifies the calibration artifact 60 (block 208). In some embodiments, the identification includes identifying one or more control points 61 of the calibration artifact 60.

[0047]

[0055] The control unit 90 determines the detected position of the calibration artifact 60 based on the movement of the robot 40 (block 210). The detected position is determined by matching the position of the printhead assembly 20 when the calibration artifact 60 was captured in the image data by the camera 30. For example, if the calibration artifact 60 was captured in an image frame taken at time X, the control unit 90 determines the position of the printhead assembly 20 at time X. The position of the calibration artifact 60 is then equated to the position of the printhead assembly 20 at that time. In some embodiments, this includes the time when the control point 61 was captured in the image data. In some embodiments, the position of the printhead assembly 20 is equated to the position of the TCP 26.

[0048]

[0056] In some embodiments, the detected position further includes considering an offset distance on the printhead assembly 20 between the TCP 26 and the camera 30. In some embodiments, this is necessary for the control unit 90 to equate the position of the camera 30 with the TCP 26. In one embodiment, the control unit 90 selects one or more frames from the image data. For each of the frames, the control unit 90 first determines that the position of the camera 30 is equal to the TCP 26. The control unit 90 then considers the offset distance between the TCP 26 and the camera 30 to identify the detected position of the calibration artifact 60.

[0049]

[0057] The camera 30 is then calibrated (block 212) based on the known position of the calibration artifact 60 and the detected position of the calibration artifact 60. The difference between the two positions allows the control unit 90 to calibrate the camera 30 relative to the robot 40.

[0050]

[0058] In some embodiments, calibration of camera 30 uses conventional optimization methods to determine camera parameters. The calibration parameters may include one or more intrinsic and / or extrinsic parameters. In some embodiments, control unit 90 may determine the overall alignment of printhead assembly 20, the alignment of each individual printhead 22, 23, 24, 25, the operation of each individual printhead 22, 23, 24, 25 (e.g., whether the printhead is working properly), and various color gamut aspects.

[0051]

[0059] 6 illustrates another method for calibrating a camera 30 for use with robotic inkjet printing. The method includes printing a calibration artifact 60 having one or more control points 61 (block 250). The calibration artifact 60 is printed using a printhead assembly 20 coupled to a robot 40. The calibration artifact 60 is printed at a known location on an object 100. The camera 30 coupled to the printhead assembly 20 is moved using the robot 40 (block 252). The camera 30 captures image data of the calibration artifact 60.

[0052]

[0060] The image data is analyzed to detect a calibration artifact 60 (block 254). The detected position of the calibration artifact 60 is determined based on the position of the robot 40 when the image data was captured (block 256). The camera 30 is calibrated based on the known position of the calibration artifact 60 and the detected position of the calibration artifact 60 (block 258).

[0053]

[0061] 7 illustrates a method for calibrating a camera 30 for use with robotic inkjet printing. The method includes determining dimensions of an object 100 in a coordinate system 99 based on a three-dimensional scan of the object 100 by a metrology system 50 (block 280). A calibration artifact 60 is printed on the object 100 using a printhead assembly 20 coupled to a robot 40 (block 282). The calibration artifact 60 is printed at a known location on the object 100 in the coordinate system 99.

[0054]

[0062] The position of the robot 40 is monitored in the coordinate system 99 as the robot 40 moves over the object 100 (block 284). A camera 30 coupled to the robot 40 moves over the object 100 and captures image data including the calibration artifact 60 (block 286). When the image data of the calibration artifact 60 is captured, a location of the tool center point 26 is identified (block 287). This location is based on the position of the robot 40 when the image data was captured by the camera 30. The camera 30 is calibrated with respect to the robot 40 based on the difference between the known position of the calibration artifact 60 and the tool center point 26 when the image data of the calibration artifact 60 was captured (block 288).

[0055]

[0063] In some embodiments, printhead assembly 20 includes a single camera 30 that captures image data. In other embodiments, printhead assembly 20 includes two or more cameras 30, each capturing image data. The positions of cameras 30 are tracked and the image data captured by cameras 30 is analyzed as described above. The detected positions of calibration artifacts 60 are determined based on image data from one or more of the different cameras 30.

[0056]

[0064] In some embodiments, the calibration process is performed by a control unit 90. In some embodiments, the control unit 90 is coupled to the printhead assembly 20 and / or the robot 40. In other embodiments, the control unit 90 is remotely located away from the robot 40 and the printhead assembly 20.

[0057]

[0065] 8, the control unit 90 includes a processing circuit 91 that operates according to program instructions 93 stored in a memory circuit 92. The processing circuit 91 includes one or more circuits, microcontrollers, microprocessors, hardware, or combinations thereof. The processing circuit 91 may include varying amounts of computing power to provide the required functionality.

[0058]

[0066] The memory circuitry 92 includes a non-transitory computer-readable storage medium having stored thereon program instructions 93, such as a computer program product, that configure the processing circuitry 91 to implement one or more of the techniques described herein. The memory circuitry 92 may include various memory devices, such as, for example, read-only memory or flash memory. The memory circuitry 92 may be a separate component as shown in FIG. 8 or may be incorporated into the processing circuitry 91. Alternatively, the processing circuitry 91 may omit the memory circuitry 92, for example, according to at least some embodiments in which the processing circuitry 91 is dedicated and non-programmable.

[0059]

[0067] The interface circuitry 94 transmits and / or receives signals from one or more of the system's components, including, but not limited to, the robot 40, the printhead assembly 20, and the camera 30. The interface circuitry 94 may provide one-way or two-way communication between the components.

[0060]

[0068] Communications circuitry 95 provides communications between control unit 90 and remote nodes (e.g., operator devices, servers, databases). Communications circuitry 95 transmits and receives data to one or more remote nodes. A clock 89 is used to track the timing of movements of robot 40 and / or printhead assembly 20.

[0061]

[0069] The user interface 96 allows a user to control one or more aspects of the system during operation. The user interface 96 includes one or more input devices 98, such as, but not limited to, a keypad, a touchpad, a roller ball, and a joystick. The user interface 96 also includes one or more displays 97 for displaying information about a test and / or for an operator to input commands to the processing circuitry 91.

[0062]

[0070] In some embodiments, a control unit 90 controls the overall operation of the calibration system. Additionally or alternatively, one or more of the components may be controlled by a user.

[0063]

[0071] The present application considers the challenges of inkjet printing, particularly large scale inkjet printing using a large robot 40 sized to extend over a portion or the entire object 100. The present application addresses challenges of inkjet printing including a very low tolerance for error in ink application before visible defects occur. One or more cameras 30 monitor the inkjet printing and detect visible errors. Calibration of the cameras 30 provides localized, low latency visual monitoring to minimize visible printing defects. The cameras 30 are configured to identify various errors in inkjet printing, such as, but not limited to, nozzle stalls between overlapping passes of ink application and motion system errors.

[0064]

[0072] In some embodiments, multiple different calibration artifacts 60 are stored in memory circuit 92. Each of the calibration artifacts 60 is applicable to detect a different aspect of the camera calibration. Control unit 90 identifies one or more calibration artifacts 60 to be printed on object 100 based on a desired aspect of the camera calibration. In one embodiment, control unit 90 receives input from a user regarding an aspect of the calibration and prints one or more applicable calibration artifacts 60 based on the input.

[0065]

[0073] The present invention may be practiced in other ways than those specifically described herein without departing from the essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes that come within the meaning and range of equivalency of the appended claims are intended to be embraced therein.

Claims

1. 1. A method of calibrating a camera (30) for use with robotic inkjet printing, comprising the steps of: printing a calibration artifact (60) including one or more control points (61), the calibration artifact (60) being printed using a print head assembly (20) coupled to a robot (40), the calibration artifact (60) being printed at a known location on an object (100); using the robot (40) to move a camera (30) coupled to the printhead assembly (20) to capture image data of the calibration artifact (60); detecting the calibration artifact (60) from the image data; determining a detected position of the calibration artifact based on a position of the robot when the image data was captured; and calibrating the camera based on a known position of the calibration artifact and the detected position of the calibration artifact.

2. The calibration artifact (60) includes one or more control points (61) located at known control point locations, and the method comprises: determining the detected positions of the control points (61) from the image data captured by the camera (30); and 2. The method of claim 1, further comprising calibrating the camera based on the positions of the control points of the calibration artifact and the detected positions of the control points of the calibration artifact.

3. generating a scan path for the robot (40) to move the printhead assembly (20) over the object (100); and 2. The method of claim 1, further comprising capturing the image data of the calibration artifact while the robot moves the printhead assembly along the scan path.

4. The method of claim 1 , further comprising capturing a three-dimensional scan of a surface of the object (100) using a metrology system (50) prior to printing the calibration artifact (60) at the known location.

5. The method of claim 1 , further comprising determining a movement of the robot (40) within a metrology coordinate system based on the three-dimensional scan of the object (100).

6. The method of claim 1 , further comprising determining the location of the robot (40) based on a tool center point (26) of the printhead assembly (20).

7. The method of claim 6, further comprising calibrating the camera (30) based on a known distance on the printhead assembly (20) between the tool center point (26) and the camera (30).

8. The calibration artifact (60) is a first calibration artifact (60), and the method comprises: printing a further calibration artifact (60) at a known location on said object (100); capturing further image data of said further calibration artefact (60); and 2. The method of claim 1, further comprising calibrating the camera (30) relative to the robot (40) based on a difference between the known position of the calibration artifact (60) and the tool center point (26) at the time the image data of the calibration artifact (60) was captured.

9. The method of claim 1 , wherein capturing the image data of the calibration artifact (60) comprises capturing the image data with a line scan camera (30).

10. 1. A method of calibrating a camera (30) for use with robotic inkjet printing, comprising the steps of: Determining dimensions of an object (100) in a coordinate system (99) based on a three-dimensional scan of the object (100) by a metrology system (50); printing a calibration artifact (60) on the object (100) using a print head assembly (20) coupled to a robot (40), the calibration artifact (60) being printed at a known position on the object (100) within the coordinate system (99); monitoring the movement of the robot (40) within the coordinate system (99) while the robot (40) is moving over the object (100); using the robot (40) to move a camera (30) over the object (100) and capture image data of the calibration artifact (60); determining a location of a tool center point (26) of the printhead assembly (20) when the image data of the calibration artifact (60) was captured based on a position of the robot (40) when the image data was captured by the camera (30); and calibrating the camera (30) relative to the robot (40) based on a difference between the known position of the calibration artifact (60) and the tool center point (26) at the time the image data of the calibration artifact (60) was captured.

11. 11. The method of claim 10, further comprising calibrating the robot (40) in the coordinate system (99) of the metrology system (50) prior to printing the calibration artifact (60) on the object (100).

12. The method of claim 10, further comprising designing the calibration artifact (60) and including one or more control points (61) within the calibration artifact (60).

13. The calibration artifact (60) is a first calibration artifact (60), and the method comprises: printing a further calibration artifact (60) at a known location on said object (100); capturing image data of said further calibration artefact (60); and 11. The method of claim 10, further comprising calibrating the camera (30) relative to the robot (40) based on a difference between the known position of the calibration artifact (60) and the tool center point (26) at the time the image data of the calibration artifact (60) was captured.

14. 14. The method of claim 13, wherein calibrating the camera (30) relative to the robot (40) includes taking into account a known distance between the tool center point (26) and a position of the camera (30) on the printhead assembly (20).

15. 1. An inkjet printing system for printing on an object, comprising: a printhead assembly (20) including a plurality of inkjet printheads (22, 23, 24, 25), the printhead assembly (20) being configured to be mounted to a robot (40); a control unit (90) operatively connected to the printhead assembly (20) and the robot (40) for moving the printhead assembly (20) relative to the object, the control unit (90) comprising a processing circuit (91), the processing circuit (91) comprising: printing a calibration artifact (60) including one or more control points (61) at a known location; operating the robot (40) to move a camera (30) coupled to the printhead assembly (20) over the object and capture image data of the calibration artifact (60); detecting the calibration artifact (60) from the image data; determining a detected position of the calibration artifact based on a position of the robot when the image data was captured; and calibrating the camera based on the known position of the calibration artifact and the detected position of the calibration artifact.

16. 16. The inkjet printing system of claim 15, wherein the control unit (90) is further configured to monitor a position of the printhead assembly (20) based on a tool center point (26) of the printhead assembly (20).

17. 16. The inkjet printing system of claim 15, wherein the control unit (90) is further configured to determine the detected location of the calibration artifact (60) based on a known distance between the camera (30) and a tool center point (26) of the printhead assembly (20).

18. The inkjet printing system of claim 15, further comprising a metrology system (50) for determining a three-dimensional shape of the object.

19. 16. The inkjet printing system of claim 15, wherein the control unit (90) is further configured to identify the calibration artifact (60) based on a set of calibration artifacts stored in a memory circuit (92).

20. 16. The inkjet printing system of claim 15, further comprising a user interface (96) having an input device (98) and a display (97), the user interface (96) configured to send signals to the processing circuitry (91) to control an aspect of the calibration of the camera (30).

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