Re: Steppers or servos

["Steve Carlisle" <quatsein-at-island.net>]

 Jon, what is this fixed upper step rate, that limits EMC's
use. You did say that did you not.

Steve Carlisle

Steve Carlisle


----------
> From: Jon Elson <jmelson-at-artsci.wustl.edu>
> To: Multiple recipients of list <emc-at-nist.gov>
> Subject: Re: Steppers or servos
> Date: Wednesday, October 18, 2000 1:02 PM
> 
> 
> 
> 
> David Preston wrote:
> 
> > I am curious to know whether steppers or servo motors are better
> > suited to EMC. Perhaps someone knowledgable in this area could explain
> > the pros and cons of each, I also have ready access to numerous
> > smaller servo motors and was wondering if it's possible, and if so,
> > how difficult it would be to wire several smaller motors in parallel
> > driving a common leadscrew. Last but not least, can someone please
> > tell me if EMC can easily run a fourth and fifth axis (rotary i.e. an
> > indexing head) as well as xyz?
> 
> Well, it's not EMC really.  EMC is one of the few programs that can run
> EITHER
> servos or steppers.  There is a limit on step rate with EMC, now.
> Servos don't
> suffer this limitation.  If you want very smooth, accurate parts, I
> recommend
> servos.  A good servo amp will keep the motion smooth down to extremely
> low velocities (like .01"/min) without any stair-steps.
> 
> Wiring motors in parallel is no big deal, but COUPLING them mechanically
> 
> in parallel is more difficult.  I really don't think it is practical.
> Surplus servo
> motors in larger sizes are available at low cost, if you look
> carefully.  You
> might try eBay, where a lot of servo and motion control stuff is sold.
> 
> EMC will soon have capability of running up to 6 axes of mixed linear/
> rotary type, as well as Stewart platforms in 6 axes, I'm told.
> Some of the software components that prevented this have now
> been changed to allow the extra axes.  There is one component
> left, the kinematics routines, and work is underway now to add the
> extra axes to that.  There will probably be several versions made,
> and either scripts or configuration files that will allow you to set up
> the axes and offsets for the machine.  This should allow the complex
> calculations involving the distance between the centers of rotation
> of the rotary axes to be performed, so the XYZ-AB(C) coordinates
> can be entered in workpiece coordinates, without regard for the
> physical configuration of the stacked axes on the machine.  The
> kinematics routines will compute the necessary movements to
> put the tool where the programmer wants it on the workpiece.
> 
> When this is all working, it will move EMC a lightyear ahead
> of the other low-cost CNC's, which don't do this for you.
> 
> Jon
>