Robot Signature Calibration

You can perform robot signature calibration to compensate for robot motion inaccuracies between the real and simulated robots.

These inaccuracies are caused by inexact link lengths, link offset, and link twist parameters in the open loop linkage of the robotic device. Signature calibration is accomplished by specifying joint offsets or delta vectors.

Joint-level calibration errors account for 80% of the inaccuracies in a typical robot workcell. For greater accuracy, delta vector parameters are used to model the complete kinematic signature of the robot. These signature parameters are used by DELMIA software to modify robot forward kinematics as well as the nominal solution configurations returned by robot forward kinematics.

The combination of forward kinematics and inverse kinematics is used during uploading and downloading to the real robot to compensate for its signature. Delta vector calibration shows better proportionality to kinematic errors at each joint without the singularity problems.

This task shows you how to:

Before you begin:
  • Ensure that a data file has been created that contains the tag names, TCP locations and robot joint values for several locations as measured by a Coordinate Measuring System (CMM).
See Also
Auto ID Input File

Set the Signature Status

You can specify the signature calibration to use in forward and inverse kinematics calculations to make the simulated robot more closely match the positions of the real robot.

  1. From the Signature Calibration toolbar, select Set Signature Status
  2. From the tree or the work area, select a robot. The Select Status dialog box appears and displays the current setting.
  3. Select one of the three available options.
    • Select Signature Off to turn off signature calibration.
    • Select Joint Offsets to enable the Joint Offset type of signature calibration.
    • Select Delta Vectors to enable the Delta Vectors type of signature calibration.
  4. Select OK to save the changes.

View and Edit Joint Offset Values

You can view and edit the joint offset parameters.

Joint Offsets are used in forward and inverse kinematics calculations to make the simulated robot more closely match the positions of the real robot. These values are taken into account when jogging the robot or simulating a robot task . When the signature status is set to any value other than Joint Offsets, these parameters are ignored.

  1. In the Signature Calibration toolbar, select Joint Offsets

    Note: If the signature status is not already set to Joint Offsets you will be prompted to change the signature status.

    The Joint Offset Values dialog box appears and displays the offset values for each joint.
  2. Double-click on any displayed parameter to edit its value.
    • You can also use Shift-click and Control-click to select multiple rows, or select the column title (Joint) to edit all values at once. All selected rows must be of the same joint type (rotational or translational).
    • Select Reset to set all joint values to 0.
    The Edit Parameter dialog box is displayed.
  3. Enter the new value and select OK to close the dialog box.
  4. In the Joint Offset Values dialog box, click OK to keep any parameter changes made or Cancel to end the command without keeping any changes.

View and Edit Delta Vectors

You can view and edit the delta vector parameters.

Delta vectors are used in forward and inverse kinematics calculations to make the simulated robot more closely match the positions of the real robot. These values are taken into account when jogging the robot or simulating a robot task . When the signature status is set to any value other than Delta Vectors, these parameters are ignored.

  1. In the Signature Calibration toolbar, select Delta Vectors .

    Note: If the signature status is not already set to Delta Vectors you will be prompted to change the signature status.

    The Delta Vector Values dialog box appears and displays the delta vector values for each joint.
  2. Double-click on any displayed parameter to edit its value.
    • You can also use Shift-click and Control-click to select multiple rows, or select a column title to edit all values for the column at once.
    • Select Reset to set all values to 0.
  3. In the Delta Vector Values dialog box, click OK to keep any parameter changes made or Cancel to end the command without keeping any changes.

Auto ID

Before you begin:
  • Ensure that the Signature Status for the robot is set to either Delta Vectors or Joint Offsets before using Auto ID.
  1. Select Auto ID
  2. Select a robot in the work area.
    The Auto ID dialog box is displayed. Its controls are disabled until a data file is loaded.
  3. Click Select data file and browse to select the data file.
    The controls in the dialog box become enabled, and
    • The Tool profile selected by default should be the current tool profile.
    • Under Measurement device (CMM), the default value for Orientation should be CMM did not measure orientation.
    • The Orientation parameter under Noise parameters remains disabled, as well as the OK and Preview controls.
  4. For Tool profile(s), select the tool profile that represents the location that was measured by the CMM on the robot mount plate.
    • Select Edit TCP values to enable the displayed values for editing.
    • Select Display compass to display the compass at the TCP using the current tool profile.
    • When both Edit TCP values and Display compass are selected, you can use the compass to directly modify the tool profile.
  5. In the work area, select the product that represents the starting guess for the location of the CMM. The origin of the CMM defines what the measured coordinates in the data file are relative to.
    The Preview button becomes enabled.
  6. Specify the Orientation.
    • When CMM did not measure orientation is selected, Orientation is disabled under Noise parameters, and the tool profile orientation parameters are displayed as Invalid.
    • If the value is set to CMM measured orientation then the orientation noise should be enabled and the tool profile orientation parameters should be able to be set to "Free" or "Fixed".
  7. Specify other parameters, including:
    • Position measurement noise: An estimate of the amount of noise in the position measurements.
    • Orientation measurement noise: An estimate of the amount of noise in the orientation measurements, if applicable.
    • Reuse tag group: If selected when a tag group with the same name as the data file exists, and that tag group is attached to the selected CMM, the tag group will be reused. Otherwise, a new tag group will be created each time the Preview button is pressed.
    • The rotation and orientation directions in which the CMM to robot base transform may be adjusted.
    • The rotation and orientation directions in which the tool profile may be adjusted.
    • The joint parameters that can be adjusted.

      If the robot has a signature status set to Joint Offsets, "Free" or "Fixed" can be selected for each joint.

      If the robot has a signature status of Delta Vectors, "Free" or "Fixed" can be specified in addition to "Translational" or "Rotational." Translational means only the translational delta vector parameters are adjusted for that joint, and Rotational means that only the rotational parameters are adjusted. For linear joints only the "Translational" option is available, as there are no rotational delta vector parameters for linear joints. The "All" combo box can be used to change the value for all the parameters in that column.

  8. Select Preview.

    The Results tab becomes available to view the results of the calibration. It displays the calculated Joint Offsets or Delta Vectors. It also displays the maximum uncertainty for each parameter type or NA if no parameters in that category were fit. The number of iterations, number of data points and the RMS error are also displayed.

    • If the calibration was successful, OK becomes enabled. If the calibration failed, OK remains disabled.
    • The CMM is moved to the Base Transform location calculated by the Auto ID algorithm.
    • The Tool Profile values on the "Input" tab page are updated to the values calculated by the Auto ID algorithm.

  9. After the first calibration has completed, the input parameters can be modified and Preview can be selected again to perform a second calibration.
    The output parameters from the first calibration are the input parameters to the second calibration. This means that the joint offset values, CMM location, and tool profile offset calculated during the first calibration are used as starting guesses for the second calibration. Using this method, the first calibration can be used to fit the base and tool transform, and the second calibration to fit the signature parameters.