- Feb 26, 2020
- Reaction score
I have a question in mind. Since this is a CNC related topic I will ask it here.
Why do CNC setup requires stepper motors and ball screws with minimal backlash?
My thinking is that if we can get position feedback from DRO to motor driver the setup will be backlash free.
And you could use normal acme feed screws and DC motors. Maybe DC motors with electromagnetic brakes for holding position.
My question is, Is this possible or I my idea is totally absurd?
Your idea is "semi-absurd" nothing new and nothing old.
For static machines, like a cutoff saw, a drilling machine etc. the "position, clamp, machine, reposition, clamp .... " works and is used.
Then again low precision ball screws, timing belts, pneumatic or hydraulic actuators, rack and pinion are usually seen on automatic machines.
An electromagnetic brake does not help you much to "hold a position" if your goal is to move not to stay were you are.
The acme screw is still used in manual machines, because it holds its position. A ball screw will move, when not held in place by motor or brake.
A manual machine usually moves one axis at a time and not ( all five of them ) at the same time.
Stiffness against machining forces and cutting vibrations is not the same as measurement of a position. RM-MN gave a good explanation.
You have to drive the workpiece into the cutter and the cutter is "chiseling" steel off the workpiece. (great deal of brute force)
The backlash compensation on my machine is pretty much useless a) backlash seems to be not constant b) the stepper system is too slow to take the backlash fast enough out when direction is changed. There is only so much you can do to fix a poor mechanical system with clever software (not necessary the softwares fault)
Do not underestimate the effort it takes to make clever software.