RE: On beamline motor control

['grosenbaum@anl.gov' <GERD@anbiw4.sbc.anl.gov>]

Hi Tony,

I know about this consideration. It comes up every time anew when you plan a 
new motor control system.

I had those handwheels made for the DC-motors on X9 and there was also the 
handpot for the E-500. I noticed same as Keith Brister from CHESS that these 
handwheels haven't been used much during recent years on the encoder equipped 
DC-motor drives which can be homed. I believe the E-500 handpot is sometimes 
used to 'zero' the stepper motor equipped Huber 4-circle which has no 
encoders and thus cannot be homed. 

My conclusion and recommendation is:

if you can implement on your control computer a remote, portable terminal and 
input from a joystick (or any other device that can give the computer or the 
controller the signal to move the drive) either via the remote terminal or 
via I/O-modules then you are better off with the computer because it is much 
more flexible than the old handpot known from the E-500.

On the PMAC motor controller you can connect a hand-wheel with incremental 
encoder to the encoder input of one channel and set any other channel(s) 
slave to this 'virtual' motion. The DSP within the PMAC will make the 
selected channel follow the hand wheel directly without intervention of the 
crate controller or the host computer. You can tell the PMAC from the host 
computer the scale mapping function between the hand-wheel input and the 
slave axis. If the axis you want to move is on another PMAC-controller the 
control connection is via the crate controller. If you want to learn about 
the PMAC and slaving other motions call Tom Coleman (708-252-3657).

In general, with todays fast computer and graphical user interfaces it is 
better to use the mouse than the handwheel. It is so much more flexible. You 
can select a single motion, a combined motion (i.e. moving two motors as a 
pair e.g. a pair of slits) something you can never do with the old handpot. 
You can set the speed. Or set the amount of increment and step precisely 
through an interval with every mouse click. Or hold the mouse down and drag 
the cursor and have the update rate such that you get the same 'feel' of the 
motor following your hand that you have with the handwheel. Then with a click 
on a new drive axis move another motor without having to run back 20 m (if 
you happen to be in the optics hutch) in order to connect your handpot cable 
to another controller unit. Of course you can switch the handpot cable 
connections, too. But that is a lot of cross-switching with, say, 50 motors, 
all wired, alot of work and expensive.

Greetings  Gerd