[CAD_CAM_EDM_DRO] Which Mode is Better TORQUE or VELOCITY?????????

Hi All,

I am using a Servo dynamics DC servo Drive, I am a bit
confused about the mode of operation, there are two
modes i.e Torque and Velocity, Can you people guide me
which mode is better and what are the advantages and
disadvantages of using each mode on a closed loop CNC

Thanks

Babar

--- Jon Elson <elson@...> wrote:

> 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
>
>
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