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General Mach Discussion / Re: Optimizing Isolation Routing and Motor Tuning questions
« on: May 26, 2018, 01:01:42 AM »
Hi,
my understanding, I wish I'd kept the article from which it came, is that no matter what microstepping regime you have in place your effective resolution
is that of half stepping. The only way to really increase resolution is to have gear reduction. Your machine is and has been fine with 16 microsteps, I suggest
leave it that way but realize the true (or reliable) resolution is that of 1/2 steps.
You have already established that a small difference in mechanical conditions can change the machine. If there were zero friction, zero load and zero inertia then you could get your
0.0008 inch resolution, more realistically you might get 0.0016 inch but can probably guarantee no better than 0.0064 inch.
I use Vexta 5 phase steppers on a low lash 10:1 planetary gearbox. The 5 phase steppers are natural 500 steps per revolution or 0.72 degree. With the gearbox
that becomes 0.072 degree per step, or 5000 steps per rev. I have 5mm pitch ground ballscrews and have a step/unit of 1000 steps per mm. I could if I used
1/2 stepping improve the resolution to 0.0005 mm or 2000 steps/mm. The planetary gearbox have a maximum of 3 arc minutes of backlash or the equivalent
of 0.0007 mm or 0.7um. It didn't seem sensible to me to try to have a resolution finer than the potential backlash.
I have good and reliable resolution but because of the gearing its quite slow. My stepper and drivers go 2400 rpm no trouble so with the gear reduction that's 240 rpm
of the ballscrew, at 5mm pitch that is 1200mm per minute. You don't get something for nothing.
Craig
my understanding, I wish I'd kept the article from which it came, is that no matter what microstepping regime you have in place your effective resolution
is that of half stepping. The only way to really increase resolution is to have gear reduction. Your machine is and has been fine with 16 microsteps, I suggest
leave it that way but realize the true (or reliable) resolution is that of 1/2 steps.
You have already established that a small difference in mechanical conditions can change the machine. If there were zero friction, zero load and zero inertia then you could get your
0.0008 inch resolution, more realistically you might get 0.0016 inch but can probably guarantee no better than 0.0064 inch.
I use Vexta 5 phase steppers on a low lash 10:1 planetary gearbox. The 5 phase steppers are natural 500 steps per revolution or 0.72 degree. With the gearbox
that becomes 0.072 degree per step, or 5000 steps per rev. I have 5mm pitch ground ballscrews and have a step/unit of 1000 steps per mm. I could if I used
1/2 stepping improve the resolution to 0.0005 mm or 2000 steps/mm. The planetary gearbox have a maximum of 3 arc minutes of backlash or the equivalent
of 0.0007 mm or 0.7um. It didn't seem sensible to me to try to have a resolution finer than the potential backlash.
I have good and reliable resolution but because of the gearing its quite slow. My stepper and drivers go 2400 rpm no trouble so with the gear reduction that's 240 rpm
of the ballscrew, at 5mm pitch that is 1200mm per minute. You don't get something for nothing.
Craig