Re: [CAD_CAM_EDM_DRO] Role of Tachos in EMC / Servo Systems w/ Encoders

Hi Jack

Tachos on the motor can be used for smoother low speed control.
EMC like most controls gets velocity information from the encoders.
The only problem is that if you go really slow the encoder pulse
rate gets similarly slow and can make for Nyquist issues
and jerky motion. Having a secondary analog velocity feedback
loop with a tach can smooth this out, and it is typically
done in the amp.

EMC could possibly use analog tach information, but it
is not set up for it. Many servo amps are though. They
have the circuitry to create a feedback loop from the tach.
You still use the encoders, but you send the amps velocity
information rather than torque.

Les

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.alltel.net/~leswatts/shop.html
Surplus cnc for sale:
http://www.alltel.net/~leswatts/forsale.html

----- Original Message -----
From: <jmw@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, January 21, 2003 8:55 PM
Subject: [CAD_CAM_EDM_DRO] Role of Tachos in EMC / Servo Systems w/ Encoders


> My understanding is that EMC servo systems using motion controllers
> like Servo-To-Go or Pico connect encoders to the motion controller
> and tachometers, if present, are connected to the servo amps.
>
> Since EMC is the brains of the operation, why isn't the tacho
> feedback directed to EMC via the motion card rather than to the servo
> amps--the brawn? What use can the servo amps make of the tacho
> information? The plus side is that at least the servo amps I have are
> all set up for a tacho voltage signal, so it's one less thing to be
> interfaced to the motion control unit.
>
> This question must have come up before, but I couldn't find a
> definitive thread in the archives.
>
> Thanks in advance.
>
> Jack
>
>
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