[alma-config]Reconfiguration Times

Mon Apr 15 21:34:31 EDT 2002

I caution against trying to be too detailed in the transporter
and moving crew schedule.  You almost never gain the
increase in efficiency you expect by carefully organizing
multiple crews working on the same problem, i.e. disconnect
crews, moving crews and reconnect crews, while you do
significantly decrease the sense of team ownership and
increase the likelihood of mistakes.

The same applies to driving faster.  If there are places you
must slow down or stop and start then driving faster where
you can greater increases your risk while not shortening
your overall end to end move time.

If you have a time problem, the answer is to add more transporters
and crews not trying to squeeze more moves out of the crew
or driving faster.

Cheers
David Woody

----- Original Message -----
From: "John Conway" <jconway at oso.chalmers.se>
To: "Gie Han Tan" <ghtan at eso.org>
Cc: "Max Kraus" <mkraus at eso.org>; <alma-config at nrao.edu>;
<alma-site at nrao.edu>; <mmaimcal at nrao.edu>
Sent: Monday, April 15, 2002 4:16 PM
Subject: [alma-config]Reconfiguration Times

> Hi,
>
>
>  I have been studying the timeline document Max Kraus
> left on a 'strawman' scheme for reconfiguration using 2
> transporters which then gives a total of  4 moves per work day
> (i.e. 2 moves/antenna/day). This scheme  assumes 1 hour driving
> time (or 20km if the desired loaded speed or 20km/hr is
> achieved).
>
> Members of the configuration group wondered
> how the claimed move  rate of 2ant/day/transporter
> fitted in with the spec of 20- 30 minutes to pick up and set
> down antennas. According to Project book section 4.2.14
> the requirement is that
>
> '....when the transporter arrives to
> pick up a maximum 20 minutes elapses before the transporter
> leaves loaded with an antenna, and when it sets down a maximum
> of 30 min is allowed between when the transporter arrives
> at a pad and when it is ready to depart...'.
>
>
> In fact the estimate Max gives (see details below) is more or
> less consistent with
> that spec  (he allows 30 min dead time for the transporter at
> both set up and set down), if we also  assume a drive time of 1hour
> for the transporter.
> In his scheme, he has two driver teams  and two antenna
> teams, one such team dedicated to  preparation of an antenna
> for moving prior to transporter arrival and then loading onto
> transporter the other team doing unloading and installation.
>
>
> The two specialised teams travel quickly from pad to pad
> doing their specialised functions. This saves man-hours - having
> fixed teams associated with each transporter wastes man-hours
> since they have to spend the time in the cab while the transporter moves
> from pad to pad.  In Max's scheme all the personnel work 6hrs
> at the site, though they  start  at staggered times. I have adapted
> his scheme slightly, I have included time for the specialised teams
> to move between pads, also I have included time for the transporter
> to move to the first pad at the start of the day.
>
>
> -----------------------------------------------------------------------
>
> Proposed Reconfiguration schedule, moving 4 antennas per day
> using two transporters.
>
> Each symbol between hyphens is assumed to take 0.5hrs.
>
>
> Prep/Load team         Tr-Pr-L1-Tr-Pr-L2-Tr-Pr-L3-Tr-Pr-L4
>
> Transporter 1          Tu-Tu-L1-Tl-Tl-U1-Tu-Tu-L3-Tl-Tl-U3
>
> Transporter 2                   Tu-Tu-L2-Tl-Tl-U2-Tu-Tu-L4-Tl-Tl-U4
>
> Unload/Install team                   U1-In-Tr-U2-In-Tr-U3-In-Tr-U4-In
>
> -----------------------------------------------------------------------
>
> Key
>
> Pr - prep team  'shuts down'  antennaprepares antenna for arrival of
>      transporter.
>
> In - Install team sets up  new antennas (i.e. get it ready for
observations
>      after transporter leaves)
>
> Tr - prep or install team travels - uses fast vehicle (30-40km/hr)
>
> Ln - Load antenna 'n' onto transporter.
> Un - Unload antenna 'n' onto pad.
>
> Tu - Transporter travels to next pad -  unloaded
> Tl - Transporter travels to next pad -    loaded
>
>
> Using the above scheme all crews/drivers work 6hrs at the site
>
> -------------------------------------------------------------------
>
>
> One can question whether Preparation of antenna for move
> and Installation  take less than 0.5 hrs assumed - it would be
> nice to decide the spec for that. I didn't see anything in the
> project book, maybe there is something in the Antenna design
> documents. These in any case however don't effect the reconfiguration
> rate until  'Pr' and 'In' exceed half the drive time. Also the target
> goal for unloaded transporter motion twice that for
> loaded motion (50km/hr)  so 'Tu'
> could be reduced. However  the work sequences of the eams
> have to synchronised or the man-hours and operations costs go up
> - hence  small adjustments like that don't effect the overall
> reconfiguration time.
>
> Fundamentally in the above scheme there are 2 moves/ant/day
> because for each move there is  1hr travel (unloaded), 0.5hr pick
> up,  1hr travel (loaded), 0.5hr set down = 3hrs/move and a 6hr
> work day at the site.
>
> Its important to understand the travel time numbers
> for  the compact array, how careful do we have to drive?
> To go 200m at walking pace 5km/hr takes only 2 minutes.
> All the time lost is in  acceleration-deceleration,
> aligning on approach lasers, checking that
> blocking antennas are moved out of the way etc, etc.
> Despite the small distance I can't
> believe that the drive time in the crowded compact array
> when we are moving between antennas with metre
> clearance can safely be lower than 0.5hrs?? In this
> case we can achieve 3 moves/transporter/day - and we
> probably need another preparation/installation crew.
>
> If the time to load and unload an antenna on a transporter
> can be reduced to 15 minutes and in the compact array
> drive times are 30 minutes, then we can achieve
> one reconfiguration per transporter in 90 minutes
> or 4 moves/trans/day - and we probably need 4
> preparation/installation crews (unless these
> functions can be reduced from the estimates of 30 minutes
> which Max has  to 15 minutes in which case we make do with
> 2 crews)
>
>
> --------------------------------------------------------
>
> Is a total of 4 moves/day enough??
>
> For the largest configurations whether the proposed scheme
> is OK depends critically on what
> loaded speed  be achieved. In a Y+ design the longest moves
> are 10-12km, so a speed greater than 10km/hr is needed. The
> desired target loaded speed of 20km/hr is then well within
> requirements. However In memo 280 (Radford) for instance
> an 'effective' (including  detours, start and stop)
> loaded speed of  7.5km/hr and a ring array
> was assumed which then argued for more transporters to make the
> reconfigurations for the largest arrays in a reasonable time.
>
>
> Using continuous reconfiguration in most intermediate
> configurations  a rate of reconfiguration
> of 4 antennas/move day is adequate. A 'Full cycle' in and
> out - takes of order 306 moves (see todays memo 419
> by Otarola and Holdaway). Hence at 4 ant/move day, going
> full speed the array can go through all configurations
> in 76 days (4.8 cycles/year!). More realistically I think would be
> to make 4 moves every 2 - 2.5 days, which realistically allows  two
> full cycles per year. The other days the transporter
> and crews could be used to ferry antennas to the OCF
> or do general maintainence.
>
>  However in the compact arrays from the configuration
> point of view it may be  desirable to have significantly larger
> move rates (i.e. 6 - 8  moves/day). The reason is that
> the intermediate configurations between say the most compact
> and the first N-S extended array may not be as useful as
> for the intermediates.
>
>
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