Re: [CAD_CAM_EDM_DRO] Servo heat-sensors or paranoia?

wanliker@... wrote:

>
>In a message dated 12/7/2004 10:12:08 P.M. Mountain Standard Time,
>elson@... writes:
>
>That's why my home machine has current
>LED bar graphs on the servo amps. If an axis is binding, I'll see the
>bar graph sit
>there with a bunch of bars lit and know something is wrong.
>
>
>
>Jon,
>Is this something you can post more information about, for sale, or shared?
>thanks,
>bill
>
>

Well, I don't really sell these amps as a product. I did make the blank
boards and
all other info available, and a number of people joined the project. I
don't think
many people got them built. Here's a URL :
http://jelinux.pico-systems.com/servo.html
with photos of my home-made boards. (I later had commercially-made boards
done, but I've never updated the ones in my mill, because the ones with
the hand-made
boards are still working fine.)

Anyway, the parts cost to build one of these gets close to the cost of a
Copley
servo amp, so I never thought these would be a real commercial success.
I use an Analog Devices AD620 instrumentation amp to read the motor current
(this is needed by the current/torque loop of the servo amp, so it is
not a frill)
and also feed the current signal to an "active rectifier" circuit and an
LED bar-graph
chip (LM3914, I think). The AD620 is quite amazing, it takes a 100 V
square wave
at 100 KHz with a 100 mV signal on it, and extracts the 100 mV signal
while completely
eliminating the 100 V common mode (unwanted) pulses! But, all this
stuff costs money,
which is why these amps were not competitive. I sure learned a LOT
designing them
and getting them working, though!

If somebody really HAS to have bar graphs, I could sell them some blank
boards and
instructions on how to hook them up to their existing servo amps, though.

Copley servo amps of the 300 and 400 series have a ground-referenced
current sense
output, which could be hooked to a bar graph very easily. Most Servo
Dynamics amps
have this output available, too.

Jon