Resolution depends on your screw pitch, gearing and stepper/resolver/encoder resolution.
Accuracy is dependent on these, but also on the stiffness of your stepper / servo.
With a servo, the stiffness is something you have to tune in. And it comes at the cost of instability. That is you cannot increase the stiffness beyond a limit, then it will become unstable, make noises and wear down the mechanics.
With a stepper you increase the stiffness by applying more current. But you cannot go beyond the point where the drive or motor overheats.
With a 20mm lead, direct drive and a 200 step/rev stepper motor your accuracy will be around 0,1mm. I'm fairly sure the motor will be the limiting factor here. But any inaccuracy in your screw has to be added. Microstepping will increase your resolution, but it will not make the motor stiffer.
Acme screws and ball screws can be made to the same accuracy except that Acme screws usually must have backlash or there will be no place for lubricant.
To see how stiffness works, try to take a step motor. Apply current to it and try to turn it. It works like a spring up to the point where it cogs over. Increase the current and try again. The "spring" becomes stiffer. But important: the shaft does *not* become locked even if you increase current to maximum smoke.  |