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

John,
Currently my drivers (for this current project) are setup for 1/4
stepping. I can't say as I have hit and resonance problems with
circular interpolation, rather I suspect I have run into it during
acceleration and deceleration. Working out the accel/decel the way
I wanted to (which isn't the usual way) has proven to be the big
challenge for me. Getting a smooth transitional range to keep the
steppers for "Spazing" has been tough but I think I finally have
it. At some point further down the road I am going to have to focus
much more attention on the resonance issues as I am sure once I
understand that, I can further tweak my code for better performance.

In the meantime though, it's been a hoot of a learning experience!

Chris



--- In CAD_CAM_EDM_DRO@yahoogroups.com, John Dammeyer <johnd@...>
wrote:

>
> 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
>