Re: servo amps and power supplies; terms of endearment

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.

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?

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