Hires-microstepping drivers

Hi all,

today i received three 1/256-microstepping-drivers from IMS: [www.imshome.com]

With some of my big old 1.8

Edited 1 time(s). Last edit at 03/31/2008 03:15PM by Viktor.

I thought steppers only achieved +-5% of step angle accuracy and any additional steps were for smooth operation as such 1/10 microatepping is as good as it gets for position?

---

Ian
[www.bitsfrombytes.com]

computer hard drives use a magnetic servo, which resembles a two step motor and is entirely microstepped to access the thousands of tracks on the platter.

The shaft will always be drawn to the point where the flux matches the average current, so microstepping should give great improvements in accuracy with light loads, and good improvement with medium ones.

Of course, you need feedback for high precision with medium and high loads.

Hi Ian,

my CNC-mill at home has a resolution of 25 microns per full step or 12,5 microns per halfstep (as in the actual setup).

With this resolution i can mill in aluminium with a repeatability of +/-12,5 microns, but with a 'real' accuracy of maybe 50 microns, dependant of milling speed, mill-diameter, teeth-count and some other parameters - you can see some samples in the images in my relevant posts.

With another CNC-mill from the same vendor on my previous day-work i made an experiment and replaced the halfstep-drivers with 1/8-microstep-drivers - so i enhanced the accuracy from 12,5 to 3,125 microns.

With this higher accuracy i milled in PEEK with a mill with 0,3mm diameter some very fine details and an array of parallel V-groves with 40 microns distance and 15 microns deep.

When measured the output with a submicron capable measuring system we found a repeatable accuracy of 4 to 5 microns - that was not so bad for an aluminium-frame mill with a price of 5000 Euros!

My CNC-mill at home is from the same style but bigger, so when with a theoretical accuracy of 100 nanometers per step (25 microns per fullstep / 256) i'll achieve a micron resolution in milling, this would be super-great!!! (especially because i paid only 700 Euros for the complete system with millhead and microstep-drivers )

With the 'normal' positioning errors because of elasticity in the mechanics, excentricity in the spindle and mechanical forces from the cutting in respect to moving direction, i think this mill should be capable of a repeatability of maybe 5 microns in easy millable materials too.

But with my measuring tools at home i'm actually in the range of 20 microns, so it's anyway better, then i can sense ...

Viktor