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Browse Prior Art Database

Symbol for Orienting Scanner-Equipped Robot Arm

IP.com Disclosure Number: IPCOM000100440D
Original Publication Date: 1990-Apr-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 137K

Publishing Venue

IBM

Related People

Cato, RT: AUTHOR

Abstract

This article describes a symbol design that will allow a scanner-equipped robot arm to orient itself in relation to its physical environment. From information gathered by scanning the symbol, the robot can calculate the arm's location and angle with reference to the location of the symbol. The symbol can be used to "home" the robot arm or to locate the workpiece.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 47% of the total text.

Symbol for Orienting Scanner-Equipped Robot Arm

       This article describes a symbol design that will allow a
scanner-equipped robot arm to orient itself in relation to its
physical environment.  From information gathered by scanning the
symbol, the robot can calculate the arm's location and angle with
reference to the location of the symbol.  The symbol can be used to
"home" the robot arm or to locate the workpiece.

      A single line scanner (like the commercially available "laser
gun" scanners) is relatively inexpensive and could be mounted on the
end of a robot's arm.  The information from the scanner could be used
by the robot for identifying bar coded items (parts, boxes, etc.)
that are to be handled. The same scanner could be used in conjunction
with the symbol described here to orient the robot arm in three
dimensions in relation to the symbol.  The symbol would be attached
to different things in the robot's "environment" so the robot could
determine its arm's location and angle in reference to those things.

      The symbol would consist of a series of black and white
triangles that are interleaved, to form a trapezoidal symbol.  See
the figure.  The triangles are laid out so that a normally incident
scan across the exact middle of all the triangles (the middle line is
line 1 in the figure) will "see" equal widths of black and white.  If
the scan line is parallel to the middle line but too high (like scan
line 2 in the figure), the white counts will be larger than the black
counts.  If the scan line is parallel to the middle line but too low
(like scan line 3 in the figure), the black counts will be larger
than the white counts.

      It is assumed that the direction and speed of the laser spot
scan is known as is the time when the scan line started.  This
information can be provided by the scanner head.  It is assumed that
the scan lines are straight and that the "fan" of rays from the
deflector that form the scan line are in the same plane and that
plane (F plane) is normal to the axis of rotation of the deflector (R
axis). It is possible to closely approximate this in reality.  It is
also assumed that the dimensions of the symbol are known.

      If the scan line crosses the symbol at an angle to the middle
line, then the relationship of the black and white counts will change
as the laser spot crosses the symbol. For example, scan line 4 in the
figure  would first see large black counts and small white counts.
By the time the spot reached the other side of the symbol, the white
counts would be large and the black counts small.  Knowing the exact
shape of the triangles (angle of the sides of the triangles in
relation to each other) enables the angle of the scan line relative
to the triangles to be calculated. This would result in two possible
solutions, the other solution being line 5 in the figure.  If the
scan direction is known to be left to right, then line 4 is the only
possible scan...