Subject: Coordinating motion of several motors

From: [email-masked] (Vjekoslav Balas)
Date: 16 May 1996 15:46:00 GMT

Hi,
I'd appreciate any hints on detailed steps/functions that software/hardware
needs to perform to produce coordinated motion of several motors 
eg. for 3 axis motion.

I presume that eg. for a move from (0,0,0) (X,Y,Z) -> (10,20,5),
the motor needing to move the greatest distance will need to move
fastest and speed of the other motors will be factored down
accordingly so all motors reach end point of their respective
travel at same time. What about coordination of motor ramping
as well as your experience with "look ahead" calculations
to avoid start/stop at each new point.

Could someone please give some details on this(I am going to start with software running PC parallel port but will move to dedicated uC'(s) for optimising 
motor motion capability later). All info is appreciated.

Best regards,
Vjeko

[email-masked]

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From: [email-masked] (Bart Smaalders)
Date: 16 May 1996 21:30:18 GMT

> to avoid start/stop at each new point.

You'll want to do a bit of path planning once you know the
desired trajectory.  You'll want to determine the limiting
acceleration so you can avoid loosing path following due
to current limits or stepper torque limits; that's what
determines max speed of the endpoint.

You'll end up with Bre.... (sp?) algorithm(same as used to draw lines
on pixeled display)  if you use either encoders+servos or steppers, 
since you want to avoid error accumulations in the path...

Your best bet w/ servos is to do a velocity loop in analog hardware
and drive that with a position error from the software...

And above all, don't forget the panic button and/or limit switches
to protect yourself and the hardware from those little programming
errors :-)... there's nothing like an suddenly open-loop servo
driving a robot in the wrong direction to make one
respect those sign and overflow bits...

been there, done that a long time (1981) ago w/ servos, encoders
and a lsi (pdp) 11-24 w/ RT11, Fortran and Macro...., A/D, D/A...

- Bart

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Bart Smaalders			Solaris Clustering	SunSoft
[email-masked]		(415) 786-5335		MS UMPK17-301
http://playground.sun.com/~barts			2550 Garcia Ave
							Mt View, CA 94043-1100

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From: [email-masked] (GregHodge)
Date: 19 May 1996 21:54:17 -0400

Breshenham line algorythm (sp?)