About Tool Point Calibration

Calibration features in DELMIA products allow you to identify the sources of position inaccuracy and to modify the simulation world to match the real world. This correction allows a generic simulation developed in DELMIA products to be downloaded to different workcells that are nominally identical but which differ slightly in the locations of their parts and devices, their tool offsets, and their robot signatures.

The tool point calibration method adjusts the tool profile (Utool) of a robot based on the measurement of multiple points. The procedure consists of selecting a robot resource and a tag group representing uploaded mount plate positions. The tag group is assumed to have been generated at the robot's mounting plate (0,0,0,0,0,0) while moving the tool tip to a fixed point in space at different orientations of the robot's wrist. The user also enters an initial guess for the tool point parameters. The guess parameters should be within a few centimeters of the actual tool parameters. The calibration also requires the following information from the user:

  • Translate X, Y, Z (Free/Fixed): specifies which components of the Tool frame are to be adjusted.
  • Estimated measurement noise: an estimate of the uncertainty of the positional measurements during the calibration experiment.

Unless the resource is known to be aligned with an axis or on a plane, the [X, Y, Z] parameters should all be set "Free" during calibration. The measurement noise need only be an order of magnitude estimate, for example 0.1 mm or 1.0 mm.

Based on the selections, the robot's tool profile is adjusted in an attempt to get the tool tip to move to the same point in space from each of the different wrist orientations. The algorithm works by minimizing the mean square position error between the tool tip positions from each of the mounting plate tag points while maintaining the constraints of the ''Translate X, Y, Z'' selection.

Upon convergence, an analysis of the results is displayed:
 

  • Number of iterations: the number of iterations required by the numerical identification method.
  • Number of fitting points: the number of points used for the least squares fitting procedure.
  • Root mean square fitting error: the root mean square fitting error on the points after adjusting the tool profile to the best fit possible.
  • Maximum uncertainties: the maximum of the uncertainties for the fit on the parameters to be identified. Large uncertainty values are an indication that the experimental observation strategy was flawed - even if the RMS fitting error was small.

The positions and orientations of the tag points of the mount plate tag group are significant for this procedure. However, only the tool profile position [X, Y, Z] will be adjusted; the tool profile orientation will not be changed.