Re: [CAD_CAM_EDM_DRO] Re: Re: Two motors on one axis EMC

What if one servo motor got feedback from the other servo motor?

--- Ray Henry <rehenry@...> wrote:

>
> Hello Lars and Thomas (Comments mixed in)
> <s>
> > If you're doing servos, a Servo-to-Go card (which is EMC-compatible)
> > can drive up to 8 servos. I do not think, however, that it would
> > easily allow you to master-slave a pair of motors. Since I do not use
> > servos, I cannot perfectly advise on this.
>
> Syncing servo's will require a complete loop for each motor and a higher
> level task that coordinates them. At the conceptual level, it would be
> possible to ask the interpreter to do that gearing. Something like the
> following code if x and y referred to a pair of motors driving the same
> axis of a gantry. [g0 x21.5 y21.5] would do it for one move but each pair
> would need to exactly match throughout the code.
>
> I'm guessing here but I'd think that the task could be pushed off onto the
> kinematics. Yes it's a trivial solution -- trivkins with a twist -- but
> I think that by defining an X as an imaginary line half way between two
> parallel actuators, it would produce the correct solutions without any
> further complications. You'd need to post the question to the emc users
> list and get help from the likes of Till, Sagar, Fred, and Will.
>
> It is also possible now to push the task of electronic gearing deeper into
> the code than the two examples above. A student at NIST recently
> demonstrated this by grabbing the shaft on one motor and giving it a
> twist -- the second motor exactly followed the motion. We would have to
> help you find your way to that code and enable it for your machine. I've
> asked for a copy of the student's paper and should have that available
> soon in the integrators handbook.
>
> > I cringe when I think about trying to sync two servomotors, because
> > each motor had it's own feedback loop. For myself, I would use a
> > long-distance mechanical coupling between two leadscrew, such as a
> > precision timing belt, and have the motor turn both using the belt.
>
> You're right Thomas, this does seem like the easier route but it is also
> subject to mechanical degredation over time. Belts and mechanical
> devices wear and this will cause great stress on a large system.
>
> This is a philosophical aside for which I'll owe another burger at NIST,
> but in my younger days I constructed the most perfectly designed,
> alligned, supported and braced field wire fence for a small pasture. It
> was a marvel to behold. In a matter of a few days, that %$##@* pony,
> given to my kids, had that "marvel" looking just like every other fence
> in the county. I should not need to extend the aside into the realm of
> large machines in order for you to see the parallel.
>
> > There are other issues, such as alignment/racking of the gantry when
> > driven by two motors, synchonization of the motors and leadscrews, and
> > the cost of each possible solution.
>
> It may well turn out to be less costly to build electronic gearing code,
> and multiple drives, than to maintain the mechanical system.
>
> As ever -- hope this helps.
>
> Ray
>
>
>
> 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
>
> To visit your group on the web, go to:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/
>
> To unsubscribe from this group, send an email to:
> CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
>
> Your use of Yahoo! Groups is subject to:
> http://docs.yahoo.com/info/terms/
>
>

__________________________________
Do you Yahoo!?
Yahoo! Hotjobs: Enter the "Signing Bonus" Sweepstakes
http://hotjobs.sweepstakes.yahoo.com/signingbonus