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

I was thinking of buying some current sense ammeters - the analog meter
type that use a shunt at the back, for my power supply, but I decided
not to in the end as they were quite expensive. They are quite cool
though if you like to watch the meters bob up and down as the system
works. :)

But I'm wondering if any of this is really necessary - isn't just
placing a heat E-stop on the motor going to achieve the same effect, if
not better? For slow overheating (ie too much torque, not enough lube,
blunt tool) this will work fine and shutdown the system before damage
occurs. I'm wondering about fast failures tho.. If the servo motor
stalls, are we going to be able to sense the overheat quickly enough on
the outside or will the wires in the core go red hot before there's even
much chance for the heat to get to the outside of the motor?

If a servo stalls, how long before the smoke comes out? 3 seconds? 2
minutes? 5 minutes?

Thanks!
~Abby

> -----Original Message-----
> From: Jon Elson [mailto:elson@...]
> Sent: 09 December 2004 05:05
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: 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
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com,
> wanliker@..., timg@...
> Moderator: pentam@... indigo_red@...
> davemucha@... [Moderators]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
> aol://5863:126/rec.crafts.metalworking or go thru Google.com
> to reach it if you have trouble.
> http://www.metalworking.com/news_servers.html
>

http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there,
for OT subjects, that are not allowed on the CCED list.

NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill
List Mom List Owner


Yahoo! Groups Links