Open loop vs. closed loop control?
This is the only real weakness with my machine as I designed it. The steppers run in an “open loop” mode, which means that the computer just sends pulses downstream without really knowing whether the motors are really turning. Works well despite it’s obvious shortcomings, but about once every few weeks or so it’ll screw up and the results are always comical – if I catch it in time that is! Someday I’ll upgrade to servos, which are closed loop by definition, and this problem will go away. Another important point with open loop control is that the computer is actually directing the position of the handwheels as opposed to the actual position of the axis proper. With decent leadscrews and limited backlash this isn’t much of a problem, but I can imagine with some systems this would be a real headache. Bottom line: open loop is good enough for what I do with this machine, and that actually says a lot..
