[1]
A laser source, tuned to the application, is selected. Telecentric
laser systems are capable of supporting four lasers in the housing.
Wavelengths from
442 nm (blue) to
830 nm (infrared)
are available.
The laser is directed to a rotating polygon [2],
which creates the required "scanning” frequency to ensure 100%
inspection (coverage of the product) at the highest line speed.
The beam is folded onto the plane of inspection by a spherical mirror [3].
This mirror forces the beam to maintain a constant profile and
orientation as it travels across the product width. This “telecentric”
scanning feature is essential for reliable and repeatable results in
metallizing, coating and laminating applications.
A lens [4] focuses the beam onto the plane of the product [5]. The laser spot traverses the product, at speeds to 36 KHz (36,000 scans per second).
After
interacting with the product, the laser light is transmitted and/or
reflected and is then captured by special optical receivers. The
receiver shown is a focused receiver and is a mirror image of the
projection optics. The high-speed laser spot is “descanned” by the
internal mirrors [6] creating a stationary laser spot, which is focused on the photomultiplier(s) (PMT’s) [7].
The PMT’s [7]
convert the laser light energy into electrical video signals, which are
processed in the electronics and software of the system. Depending on
the application, multiple optical fields (i.e., bright field, dark
field, polarity shift, optical power, etc.) can be generated. These
signals are analyzed by the system. If defects occur, the light energy
changes (becomes brighter, dimmer, changes direction, coherence,
etc.). These changes are seen in the electrical signals.
