Optical character recognition (OCR) is normally the province of the PC.
However, Cognex has a compact vision sensor with an embedded OCR
application, which automotive transmission manufacturer, ZF is using to
advantage at its plant in Saarbrucken, Germany
At ZF Getriebe's plant in Saarbrucken they have switched from riveting
type plates to their transmission housings to a system that automatically
engraves the serial and parts list numbers on raised rectangular areas,
with the lettering already pre-cast into the housing. This not only
provides a permanent and reliable means of identifying each transmission
for security and product traceability purposes, but also avoids the
labour-intensive and noisy process of riveting individual plates to the
transmission housings. Once marked in this way, the engraved numbers are
checked by a machine vision system to verify both the existence and
unambiguous legibility of the numbering.
The vision system ZF chose for this application was a Cognex In-Sight
3000 stand alone vision sensor featuring embedded OCV/OCR software. The
system comprises an encapsulated processing unit with interfaces, a small
progressive-scan digital camera and a control pad. The application was
simple to set up using just the control pad and a spreadsheet interface -
no PC intervention was required at any stage.
As transmission types arrive randomly at the inspection and marking
station, the type plate surfaces differ slightly due to natural
variations in the casting process from supplier to supplier. The vision
program has a series of layers or levels, which are activated according
to the results of previous levels. For example, the program first seeks
to detect certain edges and properties of the type plate surface. If
these are not unambiguously found, a search operation for other
characteristics is automatically performed at the next program level.
The characters produced by the automatic engraver must be unambiguously
legible within a strict, adjustable quality band. The vision system
detects engravings that are too shallow or deep - and thus difficult to
read - with absolute dependability. The character evaluation system also
detects wear or damage to the engraving tool and issues a fault message
accordingly.
Five different transmission types are currently being marked and
inspected in three shifts, and a further three transmission types are to
be added soon. In a test series of 1,000 Jaguar transmissions that passed
through the system, the vision system worked 100% correctly.