Path: utzoo!attcan!uunet!cs.utexas.edu!samsung!uakari.primate.wisc.edu!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.arch
Subject: Re: Data Storage density questions
Message-ID: <2386@crdos1.crd.ge.COM>
Date: 3 Aug 90 16:07:00 GMT
References: <2635@mindlink.UUCP> <10048@pt.cs.cmu.edu> <1990Jul30.231835.13898@diku.dk> <10055@pt.cs.cmu.edu> <PCG.90Aug2155515@odin.cs.aber.ac.uk>
Reply-To: davidsen@crdos1.crd.ge.com (bill davidsen)
Organization: GE Corp R&D Center, Schenectady NY
Lines: 60


  One of the interesting control problems with moving parts of an
optical system is that the displacement of a flat plane optical part,
lens or laser, is not linear with the movement of the edge. A movement
of, say, one micron at the edge may translate into 5 microsec of arc for
the first micron, but something else for the next micro. Then if the
mirror or laser is looking at a flat plane, the displacement on the plane
caused by a microsec of angular displacement is not constant either.

  Don't quit, diagram follows:

		||
		||
		||<--------------------------- actuator (vertical move)
		||
              ================o <------------- optical device and pivot
                      :                        (such as lens, laser, mirror)
                      :
                      :
                      :
                      : <--------------------- "line of sight" to the active
                      :                        area on the media
                      :
                      :
    _________________________________________________________
                                        ^
                                        |_____ media

  While the mapping of voltage to actuator position is close enough to
linear for the active range, the mapping of actuator movement to postion
on the media is highly non-linear.

  A possible solution to this is to make an actuator which produces
constant mapping on movement to angular movement, then use a curved
media. This would make the control problems a lot simpler, at the
expense of adding a bunch of form factor problems.

  Blue sky idea: use a cylinder for media, with a bar of mirrors down
the axis, and a laser at the end.

Side view:

            ----------------

            ================          <==

            ----------------

  To access any area on the cylinder, the correct mirror is raised by
activating the pizzoelectric activator under it.  Thus seek time is
minimal. The laser then illuminates the surface as the cylinder rotates,
and the light bounces back to a sensor near the laser. As the diameter
of the cylinder increases, the area (capacity) and surface speed
(transfer rate) increase. Latency would be proportional to the rpm of
the media, and I see no particular reason why it couldn't be removable.

  Anyway that's my though for the today on the better media.
-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
            "Stupidity, like virtue, is its own reward" -me