Re: [Emc-users] DRO failureType FAGOR 0-300 (spanish made)

[Jon E. <el...@pi...>]

On 01/08/2014 10:09 AM, Peter Blodow wrote:
> Gentlemen,
>
> a little off topic, sorry: A 3 axis system of above type was given to me
> because of beginning irregularities. As it turned out, all three axis
> displays are working, but mostly show irreproducible numbers, i.e., when
> pushing a glass rule slider forward and back again to the same position,
> the display does by far not return to the start value or what's worse,
> the direction of movement is not even always detected correctly.
Do you have an oscilloscope?  You should look at the A and B
quadrature signals to see if they are clean digital signals, or
full of noisy pulses.  Several things can go wrong.  First, of
course, dirt and oils can get inside the optics.  There will be
a light source behind the fixed scale and a sensor grating
that is very close to the patterned side of the scale.  the
sensor grating has the 90 degree quadrature offset fixed
into its spacing.  If dirt or oil has gotten between the light
source or the sensor, it will reduce the light passing through
the scale.  One common failure of cheap scales is they have
friction glider pads that wear down over time and allow the
scale and sensor grating to hit, rubbing off the pattern.  This
is fatal, there is no way to repair it.  You should also check
the cables for broken wires or dirty connector contacts.
The light source may be fading.  There may be adjustments
in the read head to set the comparator level for the light
source.

Finally, since all axes are showing similar symptoms, it may
be the control unit that has the failure.  Check all power
supply voltages, and especially check for AC ripple on the
power supplies.  If the power supply capacitors have 
deteriorated,
they may be causing a lot of ripple on the supply voltages,
confusing the encoder counter.

Jon