Impulse no. 1 – 2010 (PDF) - Leine & Linde

Precision and accuracy are keywords
Words such as exposure, pattern and developing make you think of photographers and developing
labs, but they are also used by Leine & Linde’s optics department. Cleanness, quality and accuracy are
required when critical components for pulse encoders are manufactured with micrometre precision.
For an encoder to work, a code disc and
a reference pattern are needed. Once the
two components have been produced and
installed with micrometre precision in
an encoder, an LED can send a beam of
light through them. Depending on what
the pattern looks like and how fast the
encoder shaft is rotating, light pulses are
created and
then converted
into electrical
pulses. It
is these electrical
pulses
that are used
to measure
the speed or
position of the
pulse encoder.
”On Time is a key concept for this department.
The customer must get their product
when they want it,” explains Resadija
Saljunovic at the optics department. In
this article we follow Resadija as she
shows us round the production process
that is central to Leine & Linde’s pulse
encoders.
Leine & Linde manufacture on demand
from customers and do not keep stocks
of code discs. This means that planning
is crucial, as all line counts between 1
and 10,000 can be manufactured, even in
small batches.
Once the daily planning is finished, the
work list for the day is printed out, with
information on which variants of code
discs are to be produced. They are made
of either glass or plastic material, using
special exposure equipment developed
in-house. An original pattern is used in
the manufacturing process, and it is the
appearance of the original pattern that is
copied onto the actual code disc.
As the entire work process is extremely
sensitive to dirt particles, all work is
performed in a cleanroom.
After exposure, the code disc undergoes
a development process in order to
develop the pattern copied during the exposure
process. Developing is performed
using an automated machine that lowers
the code discs into various tanks containing
developer and water.
It is important that there are no spots
left on the code discs from water or
chemicals. So the machine does not just
develop the code discs; it also washes
and dries them.
”It’s like spots being left on a glass
after it has been washed. There must be
absolutely no spots like that on the code
discs, because that could disrupt the
pulse encoder’s function,” Resadija explains.
Once developing is complete, the code
disc has been given its special pattern
and is ready for inspection.
”Here it’s important to be extremely
accurate, as the slightest error in the
pattern can cause errors that lead to the
finished pulse encoder not working properly.
It is partly a visual assessment of
results, which demands skilled and experienced
staff. In addition, all code discs
are checked in an automatic system for
their optic signal quality. Therefore, accuracy
and quality are two keywords for the
optics department,” Resadija says.
After the code disc has been made a
reference pattern is also required so that
the finished pulse encoder will have the
right function. The reference pattern
is developed on a piece of glass that is
glued firmly inside the pulse encoder.
This gluing is performed by a gluing robot,
and once it is finished the reference
pattern is exposed on the piece of glass. It
is extremely important for the reference
pattern to be perfectly straight so that it
can function correctly with the code disc.
The piece of glass with the reference pattern
undergoes the same process as the
code disc, with exposure, developing and
inspection.
”Just as in the code disc work, there
is a visual assessment in the inspection.
A skilled and experienced eye checks
whether there are any errors in the pattern.
No quality without accuracy,” explains
Resadija.
Finally the code disc and reference pattern
are installed in the encoder. Here too
precision is a keyword. The code disc is
centred on the encoder shaft and if this
is not done properly there is an accuracy
error.
Using special equipment, Resadija
centres the code disc in its correct position
on the shaft, extremely precise work.
The maximum permitted deviation from
the nominal position is 4-8 micrometres.
By way of comparison, a single hair is
around 50-70 micrometres thick.
When the centring work is finished,
the glue holding the code disc to the
encoder shaft is hardened using UV light,
and the department’s work is done. The
finished robust optic module then moves
to final assembly, where the complete
encoder is assembled.
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