It uses the same principle as the tactile seam tracker but instead of a stick which touches the joint, it has a laser beam which scans the joint all the time. The slides move according to what the laser detects.

 The price of this system is higher than a tactile one, but it is much more powerful because it can work on any type of joint. It can also be programmed for multiple steps or work in very difficult access places, as tank welding or spiral pipe machines.