Tool Centre Point (TCP) - The tool centre point is located either on the robot, or the tool. Typically the TCP is used when referring to the robots position, as well as the focal point of the tool. (e.g. the TCP could be at the tip of a welding torch) The TCP can be specified in cartesian, cylindrical, spherical, etc. coordinates depending on the robot. As tools are changed we will often reprogram the robot for the TCP.

Robot calibration is the process of determining the actual values of kinematic and dynamic parameters of an industrial robot (IR). Kinematic parameters describe the relative position and orientation of links and joints in the robot while the dynamic parameters describe arm and joint masses and internal friction.

A calibrated robot has a higher absolute positioning accuracy than an uncalibrated one, i.e., the real position of the robot end effector corresponds better to the position calculated from the mathematical model of the robot. Absolute positioning accuracy is particularly relevant in connection with robot exchangeability and off-line programming of precision applications. Besides the calibration of the robot, the calibration of its tools and the workpieces it works with (the so-called cell calibration) can minimize occurring inaccuracies and improve process security.

Calibration features in DELMIA products allow the user 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.

Tool Point command for robot tool point Calibration

This 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 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.
• Max 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.

 Note : 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.    

 Prerequisites: 

For this command to be executed the following are needed:

• A Robot with a predefined Tool Profile.
• A tag group containing tag points to represent the calibrated points that are uploaded from the measurements in the actual robotic setup. The Tag group is assumed to have been generated at the Robot's mounting plate while moving the tool tip to a fixed point in space at different orientations of the Robot's wrist.

UI Buttons: The button for this command is in the OLP tool bar with command title “Calibrate ToolPoint”.

Use Case :

 1) User will first be prompted to select the Robot, which is to be adjusted.

 2) Once the Resource has been selected, a dialog box showing the current TCP values is popped up.

The position of the TCP is shown by a magenta colored co-ordinate system as indicated in the image below.

3) The user will then be prompted to select a Tag group which represent the simulation points that needs to be adjusted. This Tag group is assumed to have been generated at the Robot's mounting plate while moving the tool tip to a fixed point in space at different orientations of the Robot's wrist. The tag group can be selected either from the PPR tree as shown below or by directly picking any tag point.

4) Once the tag group has been selected, a Dialog box will be displayed allowing user to input the following parameters:

Here user can pick the valid Tool Profile (Utool) for the selected Robot from the list. Then the Robot Tool Profile will be adjusted in an attempt to get the tool tip to move to the same point in space from different wrist orientations. Upon convergence, the following dialog box will be displayed showing an analysis of the results. The initial and calibrated positions of the TCP are also shown by two co-ordinate systems.