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Automatic Realtime Minimization of Pattern Stitching Error Caused by Change of Velocity Vector in a Raster Plotter

IP.com Disclosure Number: IPCOM000106692D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 120K

Publishing Venue

IBM

Related People

Lin, HT: AUTHOR

Abstract

Disclosed is an apparatus that can automatically correct pattern stitching error resulted from changing table scan direction or variation of table velocity. This technique can significantly increase system throughput and improve output quality.

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Automatic Realtime Minimization of Pattern Stitching Error Caused by Change of Velocity Vector in a Raster Plotter

      Disclosed is an apparatus that can automatically correct
pattern stitching error resulted from changing table scan direction
or variation of table velocity.  This technique can significantly
increase system throughput and improve output quality.

      Referring to Fig. 1, the artwork on the workpiece is composed
of butting strips with fine traces.  This plotter uses bidirectional
scanning to increase throughput.  For example, the head lays down the
odd number strips by scanning in the positive direction using
constant velocity and even number strips in the negative direction.
Normally the start of trace is triggered at the instant that the head
reaches the designated located above the workpiece.  However, signal
propagation time and other system preparation requirements resulted
in a constant amount of time delay (td) before the first pixel
actually strikes the workpiece.  Since the head is moving during this
time period, placement error of dX for the odd number strips and -dX
for the even number strips are made.  Thus a total stitching error of
2(dX) occurs between two adjacent strips.  For a relatively small
workpiece, it is also desirable to remove the restriction of laying
down traces only during constant velocity head scan.  This can
further enhance the throughput of these type of plotters.  The reason
is that acceleration and deceleration time of the head (or stage)
constitutes a significant portion of the total scan time.  Allowing
the plotter to lay down traces during the "non-constant" velocity
time period causes even further complication in the stitching
problem.  The value dX no longer depends solely on td but rather a
function of the instantaneous head scan velocity and td; that is:

         dX = f(X(t)<td)          Formula 1
where X(t) = Instantaneous head position at time t

         X(t) = v(t) = Velocity of head at time t

         X(t) = a(t) = Acceleration of head at time t

      The simplified schematic shown in Fig. 2 is a hardware
implementation of the solution to Formula 1.  The X Count Up and
Count Down signals that are used for head position feedback is
modified by custom hardware to account for the position error caused
by td with Head scan veloci...