Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!unmvax!intvax!mack
From: mack@intvax.UUCP (Michael J. McDonald)
Newsgroups: comp.robotics
Subject: Re: stepper motor sychronization: need help
Message-ID: <3743@intvax.UUCP>
Date: 30 Apr 91 01:07:45 GMT
References: <2350@wet.UUCP>
Organization: Sandia National Labs, Org. 1411, Albq, NM
Lines: 30

> 
> I need help with a very standard problem in motion control.
> (like a plotter or CNC XY table).
> 
> [a] I want axis A to go 20000 steps.
> [b] I want axis B to go 13000 steps in the same time as axis B so
>     that a straight line results.
> [c] assume a constant acceleration rate of 1000 steps/s*s is given
> 
> What would the algorithm look like during acceleration?
> 

jj
axis. That is, if axis A and B both accelerate at the same rates,
then one of the axis will get to a constant speed before the other
and thereby put your motions out of sync. 

Think about your problem thus:

1) axis B must always move at 13/20-ths the speed of axis b.
2) The velocity profiles of both axis will be a trapezoidal, i.e.,
   the velocity will ramp up at a constant rate for t seconds
   then stay constant until the move gets within t seconds of 
   terminating at which time it will ramp down for t seconds.
3) Compute the trapezoidal move velocity profile for axis A just
   as you would for making any linear move in A.
4) the velocity profile for axis B should then be 13/20ths of the
   move profile for axis A.

I hope that this approach is useful