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Browse Prior Art Database

Dynamic Position Correction by using Digital Delay Compensation for High Speed Laser Beam Steering

IP.com Disclosure Number: IPCOM000106851D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 137K

Publishing Venue

IBM

Related People

Lin, HT: AUTHOR

Abstract

Disclosed is a high precision programmable digitally generated signal delay used to fine tune Laser beam position. This technique can dynamically compensate for any undesirable mechanical perturbation in a precision positioning system.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 45% of the total text.

Dynamic Position Correction by using Digital Delay Compensation for High Speed Laser Beam Steering

      Disclosed is a high precision programmable digitally generated
signal delay used to fine tune Laser beam position.  This technique
can dynamically compensate for any undesirable mechanical
perturbation in a precision positioning system.

      Described is a highly repeatable, accurate and fast method for
compensating the finite system response of a positioning system.  For
most electromechanical devices, the system response time is fairly
long (usually at least several milliseconds).  This limits the
ability of the system to react or correct for any internal or
external perturbation.  In a high precision positioning system, this
could mean that one of the axes drift out of its desired position for
a fraction of a second.  This could cause severe quality problems in
equipment that uses Laser for drilling, cutting and plotting.

      A typical basic system configuration used for Laser application
is shown in Fig. 1.  This scheme consists of a Laser source and Beam
Modulator 1.  The switched transmitted Laser Beam 2 enters the Laser
Beam Deflector 3 that is used to form multiple Laser Beam Position 5.
Finally, the Laser Beam strikes the Workpiece 4.  In this type of
system, this usually consists of a minimum of three axes of motion:
A Table Scan Axis X (Item 7); A Table Index Axis Y (Item 8) and the
Laser Beam Deflection Axis y (item 3) which is made much faster than
the other two axes.  Laser beam deflection can be accomplished by
techniques such as Rotating Polygon, Vibrating Galvo or AO (Acousto
Optical) Deflectors, etc.  Scanning Axis X is used to generate Sync
pulse to provide synchronized timing for the rest of the system.

      Consider a target point P(Xo, Yo) on the Workpiece 4.  In order
for the Laser Beam 5 to strike this location, one must have:

                       Yo = Y + y

                       Xo = X
where

Y = Present location of Index Axis Y (Item 8)

X = Present location of Scanning Axis X (Item 7)
y = Present location of the Laser Beam Deflection (Item 3)

      Assume a small perturbation e(t) is injected into the stem
during scanning.  At time t, the Scanning Axis 7 reaches point X and
the Laser firing sequence starts, but the actual position of Index
Axis 8 is Ya instead of Y, i.e.,

                       YA = Y + dY

   and
                       dY = f(e(t))
i.e., dY is a function of e(t) and is a non-zero error

     Therefore, the target that Laser Beam 5 strikes is P(Xo, Y+dY+y)
instead of P(Xo, Yo) as described.  One way of correcting this error
is by adding a compensation factor dy to the Laser Beam Deflection
Axis with the net result of canceling dY; i.e.,

                          Ya = (Y + dY) + (y + dy)

   and providing    dY = -dy

   then     ...