Reference frame and tool frame

RoboDK provides some utilities to calibrate reference frames and tool frames. These tools can be accessed from UtilitiesCalibrate Reference frame and UtilitiesCalibrate Tool frame respectively.

Robot Calibration LaserTracker - Image 48

To calibrate a reference frame or a tool frame (also known as User frame and TCP respectively) we need some robot configurations touching 3 or more points, these robot configurations can either be joint values or Cartesian coordinates (with orientation data in some cases). It is recommended to use the joint values instead of the Cartesian coordinates as it is easier to check the real robot configuration in RoboDK (by copy-pasting the robot joints to the RoboDK main screen).

Tool calibration

Select UtilitiesCalibrate tool to calibrate the TCP using RoboDK. We can use as many points as desired, using different orientations. More points and larger orientation changes is better as we will get a better estimate of the TCP as well as a good estimate of the TCP error.

The following two options are available to calibrate a TCP:

oBy touching one stationary point with the TCP with different orientations.

oBy touching a plane with the TCP (like a touch probe).

It is recommended to calibrate by touching a plane reference if we have to calibrate a touch probe or a spindle. This method is more stable against user errors.

If the TCP is spherical, the center of the sphere is calculated as the new TCP (it is not necessary to provide the sphere diameter).

Robot Calibration LaserTracker - Image 49

The following steps must be followed to calibrate the TCP with a plane (as seen in the picture):

1.Select the tool that needs to be calibrated.

2.Select the calibration method”Calib XYZ by plane”.

3.Select calibrate using “joints”.

4.Select the robot that is being used.

5.Select the number of configurations that we will use for TCP calibration (it is recommended to take 8 configurations or more).

6.Select an estimate of the reference plane. If the reference plane is not parallel to the robot XY plane (from the robot reference) we must add an estimate of this reference plane within ±20 degrees. The position of this plane is not important, only the orientation.

Robot Calibration LaserTracker - Image 50

7.We can start filling the table of joint values. We can fill it manually or by doing copy/paste with the buttons (as shown in the image). We can also use the button “Get Jx” to get the current joint values from the robot in the simulator. If we are getting the joints from a real robot connected to the robot we must first select “Get current joints” from the robot connection menu (see image attached or the appendix for more information about connecting a robot with RoboDK). It is strongly recommended to keep a separate copy of the joints used for calibration (such as a text file, for example).

Robot Calibration LaserTracker - Image 51

8.Once the table is filled we will see the new TCP values (X,Y,Z) as the “Calibrated TCP”, towards the end of the window. We can select “Update” and the new TCP will be updated in the RoboDK station. The orientation of the probe cannot be found using this method.

9.We can select “Show errors” and we will see the error of every configuration with respect to the calculated TCP (which is the average of all the configurations). We can delete one configuration if it has a larger error than the others.

10.We must manually update the values in the real robot controller (X,Y,Z only). If this TCP will be used in a program generated by RoboDK, it is not necessary to update the values in the robot controller.

Reference frame calibration

Select UtilitiesCalibrate reference to calibrate a reference frame. It is possible to set a reference frame using different methods. In the example of the figure, a reference frame is defined by three points: point 1 and 2 define the X axis direction and point 3 defines the positive Y axis.

Robot Calibration LaserTracker - Image 52