Originally developed back in 2007, our theta axis calibration system is rather unique. The difficulty with head mounted dispense tips that rotate is that the tip really needs to be compensated during all degrees of rotation. A fixed dispense tip is relatively easy to calibrate - check X, Y, and Z offsets and tip diameter and you can readily generate a real world offset to the dispense tip. If the tip rotates, these offsets no longer apply.
In order to calibrate a tip with a bend you also need to consider the distance from the center of rotation to the orifice (what we call the arm). During rotation a circle is circumscribed by the arm and from that you can derive the center of rotation. Effectively the tip has its own coordinate frame that gets applied to the pattern during run-time.
In the past, a tip with a bend might have been manually rotated into position once the head theta was in the home position. That is no longer necessary and because of our camera-based tip calibration for theta, the results are astoundingly consistent.
Equipped with information on the arm and a calibrated center of rotation, it is now possible to do some things that are quite interesting. For example, as long as the tip does not physically interfere with the part (the bend accomplishes this typically) it becomes possible to dispense on an inside radius that is smaller than the arm length!
Perhaps that last does not sound remarkable, but as with all of our applications, we attempt to use CAD data rather than modifying the dispense path to accommodate the configuration of the dispense equipment.
