Thread: Ballscrews v. acme screws
Jonathan consider this telling off.....You are far too technical for your own good sometimes, this is a hobby site for a lot of people and "Captain i just cana get fix"
:-) :-) you uni boys will learn much more once you are in the real world...LOL!
It is not a real telling off, just trying to slow you down a bitIf the nagging gets really bad......Get a bigger shed:naughty:
Just to add a few things about the ballscrews, most if not all of the low cost C7 ballscrews are actually made in Taiwan by the larger better known ballscrew manufactures, it is just the low cost ballnuts that are made in China.
Fitting a spring between the nuts while eliminating the backlash is not done commercially because it causes early wear.
There are a few ways to eliminate backlash and the best way is to have two nuts with a spacer between the nuts and the thickness of the spacer accurately place the balls on opposite sides of the thread.
As long as you look after the ballnut and screw by lubricating it, it will last for years even if you push it hard.
The argument of the spring takes up the slack when the nut beds in or wears is a bit daft because if you look after the nut, it shouldnt wear, especially on a hobby machine.
I have known 20 year old machines that are worked hard and still maintain good repeatable accuracy with a good ballscrew.
The low cost chinese ballnuts are ok for hobby use but i would not even consider them for a production machine.Visit Us: www.zappautomation.com
If possible take a year out during the course to get industrial training. You will have much more to offer a potential employer.
Back to the topic:
Your quote "True, but that cannot apply in out (sic) case as we use step/dir drivers which can only ever be commanded to move one micro-step at a time" is not quite true.
Consider the case where the motor is stationary and you try to move it one microstep. If the torque when microstepping isn't sufficient to overcome the friction the motor stays where it is. You now try to move it another microstep. Now the torque produced by the motor is increased (almost doubled for fine microstepping). Each microstep asked for increases the torque (up to a maximum of 70% of the full step torque) until the motor is able to rotate. The positioning may thus lag behind the desired position by several microsteps.
The drive waveform is only sinusoidal during continuous motion.
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