Re: [CAD_CAM_EDM_DRO] Re: Re: Re: Electronic Lead Screw & Power Cross Feed | Poor Man''s CNC ?

Chris Brick wrote:

>Ron,
>
>
>
>>Don't have an explanation of how it can do this in regard
>>to speed but, it does it. When first started using encoder counts to
>>monitor position, the concern was timing constraints. Now they aren't
>>given much attention after three machines have exceeded the 22.5k
>>mark without any issues.
>>
>>
>
>Any chance you can give an explanation of how the encoder board injects
>position into mach3? Is the encoder position updated in mach three
>during every cycle or is your board calculating some position
>information and doing a comparison to mach's position information?
>
>I've got a project coming up that could really use some position
>feedback. I'll be using mach3, geckos, and servos.
>
>

As I understand it, Mach3 compares encoder position against commanded
position 18 times a second. (That sounds like the timer interrupt on
the PC.)

Well, I have an arrangement that does the same thing, using EMC. See
http://jelinux.pico-systems.com/univpwm.html for info on how it reads
encoder position. The PC has the servo loop running through it.
I've run one setup at around 380,000 encoder counts/second.
Actually, you can't even do that with a Gecko drive, it only goes
up to 250,000/sec. I use this board with my PWM servo amp
http://jelinux.pico-systems.com/pwmservo.html which is actually cheaper
than a Gecko drive. With this system, the following error is checked every
servo update cycle, normally 1000/sec, but that rate can be increased
if you need to. It also allows a sliding scale of following error, so that
more error is allowed at higher speeds, less when moving slower.
This allows you to permit greater errors on rapid traverse than you
would want on a cutting move. I was able to get following error down
to .00005" even above 30 IPM on the particular machine I mention above.

I have made up some complete drive systems, see
http://jelinux.pico-systems.com/smallpwm.html

Jon