You can't pull the X and Y axis when using steppers. So the only way it will get out of alignment is is you force it to skip a tooth on the belt or skip a step or two. This happening during a print usually means something else is majorly wrong (Fluffy is sitting on the print bed).
In either case, using DC motors or steppers, if something forces it to move out of alignment during a print, the print is still F'ed unless it is a real quick interruption like your hand got in the way. In which case steppers will probably smash your hand and keep on printing. Anything prolonged will screw up the print in either case.
And frankly there is really no reason this can't be done using steppers. The primary difference is that the DC motor with encoder knows exactly where it is at, or where is should be. Steppers only count rotations, meaning that if it need to move 3 inches and it is 1 rotation per inch in rotates 3 times, but can't tell you where on the X/Y table it is. You can add encoders to a stepper motor and have the best of both worlds, in fact I have a few at my shop. Example www.ebay.com/itm/TAMAGAWA-STEPPER-STEP-MOTOR-WITH-OPTICAL-ENCODER-/260292053378?_trksid=p2054897.l4275
Last Edit: Jan 3, 2015 19:37:18 GMT -5 by BeeAmaker
Some things are meant to be closed. Your mind isn't one of them.
Post by jimustanguitar on Jan 3, 2015 21:17:08 GMT -5
I think the bigger picture is that you can use any sort of motion/movement and be accurate with closed loop feedback. Not a new idea, but new-ish to RepRap and DIY CNC. You could use cheaper motors too, perhaps even more compact (less magnet poles).
I agree that skipped steps don't happen easily, but it would be interesting to use true feedback on something that can skip steps like the extruder. (one more thing to hang with bungees right?)