RE: [CAD_CAM_EDM_DRO] Re: Why is the push to such high step rates (Grex and Arc100)?

Thanks Chris,

The article listing has my original interrupt routine. The source code in
the zip file has the much improved (after a chat with Art Fenerty) code.
The latest int.c is now also posted in the files area.

On the subject of micro-steppers verses full or half step modes. There are
lots of products out there that do fine with full step drivers. Automation
positioning is one of those since the designers can choose the step rate so
that resonance isn't an issue.

However for CNC motion, drawing a circle takes each motor through a wide
range of speeds and it's almost certain that the resonance point will be
touched at some point. If the load on the motor is high enough at that time
it could lose steps.

A micro-stepper gets around that. For the ELS I use the LMD18245 which has
a 4 bit D/A converter to set up 15 voltages. I can make a reasonable
approximation of a sine wave for driving the motor with 8 micro-steps per
step. If I do an advanced version of the ELS I'm tempted to change to an 8
bit D/A. Not to get 256 uSteps per step but so if I do decide to use 16
uSteps per step I can pick 16 out of 255 possible voltages to get a closer
approximation to the sine wave. The possibility of changing to a different
table at different rates to deal with specific motor issues also becomes
possible.

Years ago when I used the Parker Compumotor linear steppers I learned that
the stepper motor and the drive had the same serial #. Matching the motor
to the drive can also improve things.

Cheers,

John Dammeyer

>
>
> Hi John,
>
> By the way, that was a great article, I learned a lot from it. The
> timing couldn't have been more perfect too as I was in the middle of
> doing some motion control code.