[mmaimcal]Re: Antenna Acceleration

[MORITA, Koh-Ichiro]

Dear All,

Thank you for your discussion about antenna fast motion.
This is quite helpful for me.

Richard Hills wrote:
 > I very much agree that a simple servo loop working on position error
 > would certainly get into trouble trying to follow a trajectory like
 > this.  My simple-minded understanding of the way round this (which I
 > hinted at in my earlier message) is that the servo should look at the
 > actual velocity, acceleration and "jerk" required, as well as the
 > position, and work out what current it should apply to the motors to
 > achieve this.  It won't get it perfectly right but it should be close,
 > because of imprefections in the system and the things you point out like
 > differences between antennas, etc.  The position servo then has to deal
 > with these imperfections.  We did this at a simple level on JCMT (there
 > we were just using "feed-forward" of the velocity but not the
 > acceleration) and it works reasonably well when properly tuned up.
 > We found this was better than having two modes - one for rapid motions
 > and one for e.g. tracking a given object.

I prefer to this concept.  Only what I am worring is that current
control interface specification is enough to do so.
Thus, for ACA antenna, we need to make a realistic simulation
suggested by Robert.  If someone already did these things,
please let me know.

Jeff Mangum wrote:
 > So, a more useful exercise would be to do a better job of specifying
 > the fast motion requirements (fast switching, total power OTF, and
 > interferometric OTF).  What is missing in the current prototype
 > antenna specs are things like:
 >
 > -- Duty cycle for OTF.
 >
 > -- Specific turnaround time for OTF.
 >
 > -- Tracking tolerance.
 >
 > For example, saying that the antenna should turn around during an OTF
 > raster "as fast as possible" is not a specification.  This requires a
 > number, which should derive from a duty cycle requirement.

Jeff, we already have such specification about OTF in the
calibration chapter in the project book.  Do you mean we need
more detailed requirements?

Cheers,
Koh-Ichiro