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HOW TO DO OBJECT-BASED CALIBRATION

Table of Contents

This article is applicable under the following conditions:

TMflow version: 1.76.6300 or later

TM Robot hardware version: All

Please note that, depending on the TMflow version, the user interface and the operation procedure may differ.

When to do calibration #

  • Large and small calibration plates are both used to create a workspace during fixed positioning. If any of the calibration plates is > 30 km away from the camera, causing the camera to produce a low-resolution image of the plate, then the plate cannot be clearly identified. This prevents the user from calibrating the workspace correctly.
  • Object-based calibration is applicable to the eye-in-hand (EIH) setup only, which employs the difference in the robot servoing movement to calculate the relative relationship between the object and the TM Robot, eliminating the need to create a workspace.
  • An object for calibration that has a definite shape and lacks symmetry is easier to position accurately.

Causes of failure to create a workspace #

  • The working distance is > 30 cm.

  • If the camera’s resolutions are set to 1280×920, it produces low-resolution images.
  • If the TM Robot cannot find all points on the calibration plate, click the video link below to check out how this problem can be solved through object-based calibration.

Video 1

Tilt correction #

  • Setup:
    • If the working distance is large, the TM Robot cannot find the calibration plate when calibrating a workspace.
    • In this case, manipulate the robot to a distance where it can find the calibration plate.

  • Create a vision job
  • Select the EIH 2D camera of the robot
  • Open Camera Kit.
  • Set the camera’s parameters and select an appropriate focus value.

    • Click Tilt Correction
  • Enter the UI for Tilt Correction
  • Make sure the camera and the workspace are aligned
  • Execute tilt correction using a supplied calibration plate.
  • Select TM-Board and click Auto-Tilt.

  • Lifting the robot to the working distance
  • Manipulate the robot along the z-axis direction of the tool base to the working distance.

Editing the vision flow #

  • Select Object-based Cali.
  • Enter the editing process for the vision flow.

  • Pattern matching(shape)
    • Click Find > Pattern Matching(shape).

      • Place distinguishable and target objects at the same height as the same workspace.
      • The distinguishable object should be matched with objects with visible shapes; the features obtained through this matching are directional.
      • The example below displays a magnified TM Landmark as a distinguishable object.

      • Acquire the edges of TM Landmark and the characters printed on the landmark, and ensure its directionality.
  • Calibration
    • Finish the Find process and go to Calibration.

      • Select an appropriate movement range.
      • If the movement range is too small, the system may send a warning “Over the servoing limit.”
      • After the settings are completed, move the TM Robot to its initial position. Then click Start Calibration.
      • The robot moves to five different positions during calibration.
      • Hold the + button on the robot stick until the calibration is finished. This prevents the robot from colliding with any obstacles while on the move.
      • If the features matched are not clear enough, the yellow-colored scope of the actual object sampled becomes inaccurate, as shown in the image below. In this case, make necessary changes in the Find module.

  • Acquire the object’s base
    • After the vision flow is edited, execute the flow to obtain the robot base relative to the object—that is, the workspace of the target object.
    • Go back to the Find module, check the target object, and edit the flow for the object.

Troubleshooting #

    • Issue:
      • If the TM Robot keeps failing to match an object’s features while it is servoing the object during calibration, a dialog box will appear as follows:

    • Solutions:
      • Check whether the features matched are too sophisticated. Then go back to the Pattern Matching process and remove any feature that is difficult to match on the pattern matched.
      • Use an Enhance module to make any to-be-matched feature more visible and easier to find.
      • Set a lower score in the Find module. If the pattern is symmetrical, impose a limit on the angle for finding the pattern.

Demo with cardboard #

 

  • Setup:
    • Object-based calibration is performed using the logo “TMROBOT” printed on the top of a piece of cardboard. Then a flow is edited in ways that manipulate the TM Robot to use a suction nozzle to pick up the cardboard.
  • Tools:
    • Cardboard with a “TMROBOT” logo printed on it
    • ROBOTIQ Epick Gripper
  • Workspace
    • Decide the distance between the camera and cardboard
    • The distance between the camera and cardboard is about 40 cm.
    • The workspace cannot be calibrated through fixed positioning.
      • Execute object-based calibration to obtain the position of the cardboard

  • Editing the vision flow
    • Open Camera Kit
      • Set the camera’s parameters and focus.
      • Place a calibration plate and do tilt correction.
    • Select Pattern Matching(shape).
      • Circle the TMROBOT logo at the center of the cardboard and the shape of the cardboard.

      • Do calibration
        • Set the movement range.
        • Start calibration.

  • Editing the flow
    • Use a vision job to find the cardboard.
    • Teach the robot where to pick up the cardboard and install a suction nozzle for the robot to fetch the object.

  • Results
    • The robot finds the cardboard and arrives at its center.
    • The robot uses the suction nozzle to pick up the cardboard.
  • Demo Video

Demo with SSDs #

  • Setup:
    • Several SSD are placed on their respective trays, object-based calibration performed using the words printed on the top of the SSDs and the shape of the drives, and the TM Robot is manipulated to use a suction nozzle to pick up the drives.
  • Tools:
    • SSD
    • ROBOTIQ Epick Gripper

 

  • Workspace
    • Set up a workspace for the SSDs.
    • The distance between the camera and trays is about 50 cm, so the trays can be entirely seen by the camera.
    • The workspace cannot be calibrated through fixed positioning.
      • Execute object-based calibration to obtain the positions of the SSDs.

 

 

  • Editing the vision flow
    • Open Camera Kit
      • Set the camera’s parameters and focus.
      • Place a calibration plate and execute tilt correction.
      • Use an Enhance module to make the SSDs more identifiable.
      • Use Pattern Matching(shape) to circle the words printed on their center and the shape of the drives.

 

  • Do calibration
    • Set the movement range
    • Start calibration

  • Editing the flow
    • Use a vision job to find the SSDs.
    • Teach the robot where to pick up the SSDs and install a suction nozzle for the robot to fetch the objects.

 

  • Results
    • The robot finds the SSDs and arrives at their center.
    • The robot uses the suction nozzle to pick up the SSDs one after another from the trays.
  • Demo Video
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