TCP and robot calibration using a single digital indicator

An automatic procedure was developed for the TCP calibration and/or robot calibration using a Bluetooh digital indicator with a flat end-point. The digital indicator is mounted on an inclined support, fixed with respect to the robot base. The tool tip is a precision ball that is moved with different tool orientations until the digital indicator shows zero displacement. By doing so, the TCP is essentially constrained to a small planar surface.
The joint coordiates corresponding to each final measurement configuration are then used to identify either the optimal TCP coordiantes with respect to the robot's flange frame (TCP calibration), or the optimal robot DH parameters (robot calibration). That is why this kind of calibration method is called self calibration.
Once the new TCP coordinates or robot parameters identified, another digital indicator fixed in a different location is used, the TCP is brought in contact with the end-point of the digital indicator, the indicator is zeroed, and then the robot brings the TCP repeatedly to the same position but with different tool orientations. The performance of the calibration is obtained by taking the measurements (deviations from zero) of the digitiral indicator in each test robot configuration.
Two different six-axis robot arms were used in this work: a KUKA KR6 and a Mecademic Meca500. Since the KUKA robot was already factory calibrated and its tool geometry not well known, there was a significant improvement when calibrating the TCP only, but no improvement when trying to calibrate the complete system. In the case of the Mecademic robot, since the measurements of the tool were relatively accurate, there was no improvement when calibrating the TCP only, but a significant one when calibrating the complete system.
The work was performed by Geoffrey Chassin, a Master's student at the CoRo lab.

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how are the Dial guage readings utilized to find the Tooltip ?? Also, with this setup, getting the tooltip with Orientation is not be possible.... So for getting orientation as well, what setup can be made just by using the Dial guages??