Re: Low cost Servo Controller

Dean Franks wrote:

> From: "Dean Franks" <dean@...>
>
> You can also run it in velocity mode, where you set a target velocity and
> ignore the absolute position registers. This would allow it to simulate a
> Servo Amp.

We're talking about the LM628/LM629 series, here.
Yes, but if you put it in velocity mode, it won't ever stop (unless you set
velocity to zero). So, what's the advantage here? Making an outboard chip
do a couple of small calculations? A pentium CPU can do the same
calculations, in full floating-point, too, 100 x faster than it could communicate
what it needs to over the ISA bus! And, it STILL is NOT looking at
motor current, which is significant, because the inductance of a typical
medium-power servo motor introduces SUBSTANTIAL lag in the
control loop. SO, you change the pulse width of the PWM amp
NOW, and the motor current, which is almost identical to torque,
changes sometime later. Oops, too late, now we're going the wrong
way!

Jon