Re: [CAD_CAM_EDM_DRO] Servos and EMC PID tunning.

ruzip wrote:

>Greatings to everyone..
>
>I'm just trying to figure out some parameters in EMC.ini file related
>to servos. Could anyone suggest anything on what king of servo
>motors/ amps should one use with Linux EMC and servo to go card.?
>

This tells us nothing. We need to know about the machine more than
the servo controller. What is the weight? (Bridgeport or Sherline, it
makes a HUGE difference!) What rapid feed rate do you intend to
achieve? What will your cutting loads be like? (Wood router or
cutting hardened steel with a 4 Hp Bridgeport Series II machine?)
Will you use ballscrews, the original Acme screws, rach & pinion,
belt drive.... ?
What sort of precision level are you looking for? (.01" for wood router,
or .0001" for making watch parts?)

Copley Controls makes some nice servo amps for DC brush and brushless
motors. You can pick up nice servo amps on eBay, but you need to
be sure of the specs before buying.

>ac/DC with /without brake etc.
>

DC brush motors are the simplest to use, and almost any servo amp for
brush motors will work, up to the current limit. "DC brushless" motors
need special encoders to provide motor commutation information to
most brushless motor amps, and so the mating of the amp and motor
becomes much more complicated. Unless you are a servo guru, it is
best to use amps and motors that were made for each other. AC
induction servo motors need yet another type of servo amp, although
standard encoders will usually work fine, there.

A brake is only needed on some Z axes where the weight of the knee
or head would cause it to crash downward when power is cut off.
Brakes are common on robot motors, and can be removed easily in
most cases.

> Another interesting issue is the PID
>tunning in EMC. Does anyone ahve any proven methed or program to do
>so? Any imput would be greatly appreciated.
>
>

Depending on the servo amp, you often have to perform tuning of the amp-
motor-machine complex first, and when it is right, you then add the computer
and positioning loop, and tune that. There are auto-tune provisions
for EMC, but the logging/graphing features of EMC allow following error
to be plotted for a move and then the PID terms are adjusted. I can advise
you on how to do this, but all the above must be solved first.

Finally, some servo amps, especially DC brush amps, require a DC tachometer
for velocity feedback. Some others don't. So, you need to provide a tach
when it is needed.

Jon