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

Roy J. Tellason wrote:

>On Wednesday 08 December 2004 12:11 am, Jon Elson wrote:
>
>
>
>>>The other terror is the idea that someone twiddles the table-gibs a bit
>>>tight, but they can still move.. So you start out on a 3 hour milling
>>>project all the time unaware that the servo amps are compensating for
>>>the extra-friction just fine.. Except for the steady 10degrees/min temp
>>>rise of the motors...
>>>
>>>
>
>
>
>>Inadequate lube could do the same. 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.
>>
>>
>
>I like this idea. Are you using an LM3914 or similar? Connected across a
>current-sense resistor?
>
>

Yes, but it is way more complicated that that. The current sensing
resistor is
actually on the servo motor wire, so it is being pulled to +70 V 100,000
times a
second. I use an AD620 instrumentation amp to separate out the 100 mV
desired
signal from the 70 V PWM pulses and bring it down to ground reference.
Then, I
have to run it through an active rectifier to make the absolute value of
the bipolar
motor current.

Jon