Tech Briefs Magazine - June 2021 - MD-5

is equipped with a complementary metal
oxide semiconductor (CMOS) type of
FPD to help obtain high-definition
images of the object. Each parameter is
designed to optimize the images' contrast
to suit the part or object that is being isolated
for inspection purposes.
X-ray sources can be generally categorized
into two types: open tube and
closed tube. An open-type X-ray source
has a few disadvantages: (a) it must be
installed along with a vacuum pump and
other associated equipment outside it,
(b) it has a high running cost due to
such factors as a short-life filament, and
(c) the radiation source itself has a large
weight. Meanwhile, in the case of a
closed tube, the X-ray generator is constantly
kept in a vacuum in a hermetic
glass container. Therefore, this type of
radiation source features a compact body
and does not need a pump installed outside
its tube. The system makes use of a
micro-focus closed-tube radiation source
featuring a lightweight body and a small
focal diameter.
2. High-Precision Geometry Design
and Control
For the geometry design of the inline
AXI system, a parallel table type has
been adopted instead of a rotary table
type (Figure 4), since the former type
can obtain CT images by changing the
physical position of the X-ray source or
X-ray camera (FPD) with respect to the
object. A rotary table type has a round,
narrow field of view for 3D data imaging,
which can lead to images being blurred
at their edges and limitations on highspeed
imaging due to the rotation speed
limit1. What is of particular importance
about this parallel table type is the positioning
accuracy of the XY-axis rotation
trajectory. That said, the Z-direction axis
positioning accuracy also matters be -
cause this system is driven in the Z-axis
direction when switching the inspection
resolution or when tracing the bow of
the workpiece under measurement by a
displacement gauge.
A high-precision guide is provided for
each axis to achieve a positioning accuracy
on the order of micrometers using
proprietary motor control technology.
The XY-axis rotation accuracy in particular
helps to obtain increasingly better
CT images with the increase in roundness
of the rotation trajectory. Serving
as the foundation are high-quality
mechanical parts mounted at the
Motion Design, June 2021
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Parameters caused
by image quality
Parameters caused
by machine elements
FPD
CCD
Z displacement sensor
Z
X-ray focal diameter
Blur
Pix size
S/N etc.
X-ray source
Z axis positioning accuracy
XY axis positioning accuracy
(Turning accuracy)
Figure 5. Parameters associated with image quality and with mechanical components.
required degree of parallelism/straightness
and the control technology based
on the programmable logic controller
(PLC) or servomotor that enables highprecision
synchronous driving. In addition,
the imaging devices are each supported
with a high-rigidity frame and
designed with a ruggedized architecture
to keep all terminal parts unaffected by
vibrations.
Thus, to obtain clear CT images, it is
important not only to pursue the abovementioned
basic performance of the
imaging devices or parameters associated
with image quality, but also to develop a
design that takes into consideration
parameters associated with the mechanical
components (Figure 5). These pa -
rameters relate to the mechanical rigidity
or weight balance of the system, the
geometry design specifying how to turn
the imaging devices, and the system
architecture for realizing high-precision
axis positioning control.
I PJ
3. Robust Correction Processing and
Algorithm
The AXI performs rapid processing
and control of sensed information - not
only in its hardware but also in its software
application developed from proprietary
reconstruction processes and algorithms
and a deep knowledge of visual
inspection systems - to achieve a high
degree of solder shape reproducibility
and improve the inspection of solder
joint surfaces. Whenever a workpiece is
brought into the system for inspection,
there will be variations in the stopping
position. For this reason, the AXI system
is equipped with a visible light source and
a camera as well as a means of correcting
variations or rotational shifts of the feed
stop position on the workpiece conveyor
using images obtained in visible light.
To accurately perform algorithmic processing,
sufficiently high precision is
required to extract the correct tomographic
positions in a reconstructed
Tomographic position extraction accuracy
Reconstructed image
Tomographic image
XYZ
XYZ
Figure 6. Images of extracted tomographic positions.
5
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Tech Briefs Magazine - June 2021

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