Re: [CAD_CAM_EDM_DRO] Closed Loop PC Based CNC

Les,

Thanks for your response, I had considered taking an approach like this.
I was not aware that Rutex was offering a brush-less drive that is
designed for 100 and 200 volt motors. This is an attractive and powerful
drive compared to the steppers.

There are a couple of questions in my mind concerning this approach
assuming that motor positioning is in close loop control at least back
to the drive.

1) Does the drive have a PID Loop to control following error
calculated between comanded steps and encoder feedback?

2) Do the drives have both Proportional and Intergral Gain (linear
error and time base error multipliers)?

3) Do the drives attempt to reduce any following error by iterating
to near zero or only monitor a "lost steps" count?

4) If the drive cannot keep up or exceeds the "lost steps" error
count does it shut down and drop a "drive ok" signal? Can this signal be
used to take the other drives off line by controlling the "drive enable"
signal to the other drives?

5) If the drives fault and go down, the control may not know and
keep chugging along like it had good sense. Is there an drive output to
the software to prevnt this?

Some other desired features possible with a closed loop system are "soft
limits" and homing based on the encoder marker pulse. I would want to
drive the axis in the direction of the home limit at traverse speed
until the mechanical limit is tripped, switch to a slow approach speed
and drive until the marker pulse (Z/ZNOT) is detected.

All in all however, I completely agree that this is a much better
approach than where we are now.

nitewatchman



Les Newell wrote:

>If you stepper solution works well apart from the lost steps then I
>would have thought your best option would be to get servo drives that
>can accept step/direction. That way you retain your front end but have
>the advantage of servo control.
>
>More and more drives these days accept step/direction. For a cheap
>solution using brushed motors try <http://www.geckodrives.com/> or
><http://www.rutex.com/us/>
>
>Les
>
>nitewatchman5 wrote:
>
>
>>I have a Bench Mill currently running with stepper motors in an open
>>loop configuration. We are running production parts in fixtures and
>>after running several parts to several dozen parts, sizes and
>>locations start to drift due to missed steps. Slowing traverse rates
>>down and extending longer acc/dec ramps helps but the problem is still
>>there depending upon cutting forces and the shear number of axis
>>reversal moves. Additionally, slowing the machine to fit the
>>speed/torque curve of the stepper motors increases the part cycle time
>>and the part cost directly.
>>
>>As a solution I want to take this machine to a true closed-loop system
>>using AC Servo Motors. While I have retro-fitted several large
>>machines (25'+ travel) with Fagor and AB 9-Series controls,
>>maintaining a PC based control presents some problems.
>>
>>A likely scenario would be to use a matched servo drive and motor
>>combination such as the Yaskawa DR-1/SGM set for each axis. The
>>encoder feedback from the motor for commutation can be redirected to a
>>Controller board in the PC for position error control. The controller
>>would output a +/-10VDC analog signal to the Servo Amps to control
>>speed and direction. The calculated following error can then be
>>intergrated into a PID Loop to control speed, torque and location.
>>
>>There are several interesting controllers on the market such as the
>>Galil, Delta Tau and Servo to Go. The Galil especially looks very
>>powerful and is sometimes found on eBay for a reasonable price. The
>>big question however is the Front-End software to drive the
>>controller, does for example EMC support these controllers?
>>
>>Advice would be appreciated, practical experience perferred -
>>theoretical suggestion catalogued. If we can find no other solution we
>>will refit the machine with a Fagor 8025M control.
>>
>>nitewatchman
>>
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>
>
>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
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>Yahoo! Groups Links
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