Re: [CAD_CAM_EDM_DRO] Please help Permanent Magnet Field Servo Motor???????????

Babar wrote:

>Two wires are the AC input of Drive 250 VAC, The other
>two wires are shorted at the motor , the other end of
>the motor is connected to the Ground.
>The response of this drive is very slow and it is
>causing troble in the form of large following error,
>any suggestion to improve the Drive's response?
>

Well, an SCR drive is limited by the line frequency. A 3-phase
SCR drive running on 50-Hz power can't get more than 300 pulses
to the motor per second. That should still be adequate for a heavy
machine, probably giving a closed-loop response out to 75 Hz or so.
What is the current limit set for on the SCR drive?

But, if it is driven by an aged CNC control, that may be what is
limiting performance. I used an Allen-Bradley 7320 control, and
its 100 Hz servo update cycle required the system response to
be awfully sluggish. Updating it with a PC-based CNC control
improved the following error as well as the dynamic response
considerably.

> what
>if I connect the two wires that are short at the motor
>to the two ends of motor instead of connecting the
>motor's one end to the ground?
>
>
>

That isn't going to improve performance. You need to find
out what the extra wires are connected to in the motor.

>Why the line reactors are needed with servo dynamics
>drive? I understand that these are simple inductors
>(am I right?)What is the selection criteria for these
>reactors?
>
>

Check the drive manufacturer's data sheets for the minimum
motor inductance. If the motor's inductance is less than that, you
need to add inductance to bring it above the minimum. Just an
example : If the drive requires a minimum of 10 milliHenries,
and the motor is 7 milliHenry, then add a 3 mH inductor in
series with one motor lead, or one 1.5 mH in series with EACH
motor lead. Either way, you get a total inductance of about 10
mH, as the manufacturer requires. They are ordinary inductors,
but they must have a current rating equal to your peak motor
current, and either have thin steel laminations or ferrite cores
to reduce heating from the PWM frequency.

Jon