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Calibration of Overlapping Camera Images for Machine Placement of Large TAB Devices

IP.com Disclosure Number: IPCOM000107381D
Original Publication Date: 1992-Feb-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 155K

Publishing Venue

IBM

Related People

Corbin, JS: AUTHOR

Abstract

This article describes a procedure whereby multiple cameras in TAB placement tooling can be calibrated one to the other such that both can emulate a single, larger field-of-view camera with increased resolution. Compared to earlier methods of relative camera calibration, this approach provides superior performance in sensitivity, speed, and accuracy.

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Calibration of Overlapping Camera Images for Machine Placement of Large TAB Devices

       This article describes a procedure whereby multiple
cameras in TAB placement tooling can be calibrated one to the other
such that both can emulate a single, larger field-of-view camera with
increased resolution. Compared to earlier methods of relative camera
calibration, this approach provides superior performance in
sensitivity, speed, and accuracy.

      Tools exist that excise and form TAB components from their reel
(or singulated) format, and position and bond the device to a
carrier.  In order to achieve an acceptable final assembly yield,
these tools perform a full component inspection prior to placement.

      CCD cameras are used for component inspection.  As the lead
count increases and pitch decreases, it becomes more and more
difficult to inspect each individual device lead. The problem is
inherent to CCD cameras, in that these discrete devices have a fixed
array of light- sensitive elements.  As the field-of-view is expanded
to include larger and larger TAB devices in a single video frame, the
resolution of the cameras is reduced.  Eventually, there is
insufficient resolution to inspect each individual lead of a TAB
device.

      One approach is to use multiple cameras to view the device with
separate but overlapping field-of-view images, and merge the images
to emulate a single large array CCD camera. One difficult aspect of
using multiple CCD cameras is the requirement that they be very
accurately calibrated one with respect to the other.  The vision data
collected by each are merged into a single vision data file, and the
inspection algorithms operate against this one file. Practically,
this means that the data from one camera must be mapped into the
frame of the other camera.  If this mapping is not accurate, the
resulting merged data file will be erroneous, and, hence, the
inspection results erroneous.

      This article describes a technique whereby each of the
inspection CCD cameras (see Figure 1) used in TAB assembly tooling
can be accurately calibrated, one to the other. Cameras 2 and 3 view
a TAB device held by the robot end-of-arm tool through a split image
prism, each camera viewing a different portion of the device.  The
two images overlap to form a single representation of the device.

      The overlapping camera images may appear (greatly exaggerated)
as shown in Figure 2.  The images may be rotated one relative to the
other because the cameras are not perfectly aligned mechanically.
Additionally, the scale factors of each camera may be slightly
different, as may be the orthogonality of each camera CCD array.  The
objective is to transform the data of camera 3 into the reference
frame of camera 2, and operate on the resulting single image data
file.

      Various camera models exist that define the mapping between
three- dimensional object data and the two-dimensional image data
tha...