Re: servo amps and power supplies; terms of endearment

My Pleasure Jack,

Quite a bit of hardware you have there!

jmw@... wrote:

>
> Alan, thanks for your reply. Some of the specs on the amp:
>
> Specifications
> Make Baldor
> Model UM4-100-2
> Power DC Buss voltage aprox. 70 to 135
> Rated at Aprox. 15Amp continuous / 25Amp peak
> Tach as used in the original application is 7 Volts per 1000 RPM
> Input signal is +- 10 volts analog
>
> This is a PWM amp, and after reading your explanation I now have a
> little better idea of what that means. Amazing that these cards can
> switch all the power running to a motor sized for a Bport class mill.
> I'd have thought there'd be something resembling a heat sink on each
> card--although there are some muffin fans on the cage.

Probably good switching transistors in the 'H' bridges, although you'd
think they'd need SOME heatsinks.

>
> Also amazing to me that three or four cards can be switching power
> from one source simultaneously. So at any one time all axis motors
> are getting the same voltage? Although they may be drawing different
> amps and getting their juice in jolts of different length and with
> different direction signals?

Yes, and remember, each motor gets power for a period of time determined
by it's PWM signal. Like having three different lamps, all with
dimmers, all run on the house 115V, but each can be set to a different
light level. Also, the voltage for each motor will take a finite time
to rise, due to the inductance. But yes, they are each on their own.

Now, do you have schematics? Are things already connected? Hopefully
someone will recognize your hardware, and be able to further assist you.
Alan

>
> Thanks.
>
> --Jack
>
> --- In CAD_CAM_EDM_DRO@egroups.com, Alan Marconett KM6VV <KM6VV@a...>
> wrote:
> > Jack,
> >
> > FOR A QUICK (simple) ANSWER; there is usually a driver for the servo
> > motors (your boards), that receive a commanded position, and an
> current
> > position (motor encoders). These two "values" are summed (added)
> > together, and the result is "correction" (error) value. This error
> > value is usually applied to a PWM (Pulse Width Modulator) circuit,
> which
> > controls the amount of "on time" of a switch sending power from the
> > power supply to the motor. Also sent is the direction for the
> motor to
> > turn (the sign of the correction value). The "switch" is usually
> an 'H'
> > bridge, a fancy electric switch to allow the motor to run in either
> > direction. Thus the motor turns, and changes the current position,
> > which reduces the correction value, and the motor gets to where it
> is
> > commanded. PID will not be discussed here!
> >
> > THAT is a quick (simple) answer, SOMEONE on this list can probably
> > identify the boards/hardware you have (what do you have?), and
> suggest
> > what you need to add! Most likely, you will need a standard power
> > supply that is of the proper voltage and current rating. Something
> to
> > match the motors (you have motors?).
> >
> > And, I'M SURE, you can get a MORE extensive, MORE accurate
> description
> > of a simple servo system, OR the one YOU HAVE!
> >
> > Hope this helps,
> >
> > Alan
> >
> >
> > jmw@c... wrote:
> > >
> > > I've got a servo amp with 4 boards, each rated to run a (permanent
> > > magnet DC servo) motor 70-100 VDC at 15 cont / 25 peak amps. The
> unit
> > > has an integrated power supply for its own requirements--but zilch
> > > for the motors.
> > >
> > > What I'm wondering is how the amp communicates with the power
> supply
> > > so as to vary the power supplied to the motors? Does the amp just
> > > tell the individual motors to run faster or slower and so each
> just
> > > pulls more or less from the well? Maybe the amp sends voltage and
> > > amperage codes to the power supply and it adjusts its output (but
> > > this would require a power chanell for each motor, right?) Maybe
> the
> > > full output of the power supply runs through the amp and four
> demons,
> > > one for each motor, regulate the flow to each motor.
> > >
> > > As I've stated before, I'm not an EE. I figure I could probably
> > > figure out how to make a simple DC power supply, but depending on
> the
> > > complexity of the controll scheme I might just try and find one
> > > surplus.
> > >
> > > As always, thanks in advance.
> > >
> > > --Jack
>