Coordinated motion of slits

["Davis, Mark via Tech-talk" <tech-talk@aps.anl.gov>]

Hi all,

We will soon be adding a couple of motors to a Delta Tau Power Brick 
controller that will control the left and right drives for a slit and I 
was hoping someone could provide me some direction about how to go about 
using the Model 3 motor interface to achieve coordinated motion control 
of the two drives on the controller itself.

 From what I learned from the Delta Tau online training videos I was 
able to use the vendor's PowerPMAC IDE to define a coordinate system 
with the two motors and two axes (one for center position and one for 
the gap), define the relationship between the motor's positions and the 
two axes, and write a trivial motion program that causes the two motors 
to move correctly in response to a change to the setpoint for the two axes.

But that is as far as I have gotten.  Ignoring for the moment everything 
but the most basic aspects of this, what I need is to have two records, 
one for the center position and one for the gap, and to have changes to 
one or both of these to cause the two motors to move as needed to 
satisfy the new settings.  I currently have such a setup where all the 
coordination of the motion is done in EPICS record logic (using the 
separate motor records for each drive), but we want to eliminate all 
that and have the controller coordinate the motion of the motors.

As I understand it, one of the basic advantages of the Model 3 interface 
for motors is that it includes support for such coordinated motion.  
And, from what little I have learned so far, it requires you to supply 
the interface with a list of the motor movements that the controller 
should execute.

Is this correct?  And if I want to avoid going around the Model 3 
interface, is this the only way to get coordinated motion that is 
managed by the controller?

If so, this would still seem to require some significant record logic 
(and possibly supporting code) to go from a change in the center and/or 
gap setting to generate and set the values in the necessary data 
structures and call the appropriate functions in the interface.

And even then, doesn't there need to be some supporting logic running on 
the controller?  As near as I can tell, coordinated motion on the Power 
Brick controller requires a motion program running on the controller, 
however trivial a program it may be.

If someone could outline the whole process and what is needed to go from 
the center and gap setpoint records to invoking the motion on the 
controller, that would be a major help and save me loads of time and effort.

-------
Mark Davis
NSCL/FRIB Control Systems Software Engineer
davism50@msu.edu