When an object is placed on the touch screen, the Kivy script POSTs the x and y percentages to the local network. To allow the grippers to interact with the object, the script must transform any touch screen point to the robot’s coordinate system.

One way to do this is to manually tell the robot where three corners of the screen are, relative to its own coordinate system.

Note: The fourth corner can be calculated. This could be reduced to two points but three gives some error tolerance.

Every time the robot’s main script liatris.py is run, it checks if a calibration file exists. If no, it runs through the calibration steps. This is started by attaching laser pointers to the grippers of the robot. Next, each arm is moved to the requested corner of the screen by manually using commands on the keyboard that Liatris defines. The lasers aid with accuracy.

After all three points are saved, a calibration file is written. These values will allow Liatris to transform any touch screen point to the robot’s coordinate system.