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Photos (3) New roll reader - pneumatic switches |
Roll perforations are detected by electro-pneumatic switches (PE switch) that operate
in the same way as the pneumatic valves in a player piano. The difference
is the output signal is MIDI data. |
Construction. Photo shows partial assembly in which neoprene diaphragms are glued to a body of
two pre-drilled and routed PVC sections that are sandwiched and glued together.
A third layer sits on top of the assembly and the PCB holding the Hall effect
switches forms the top layer. |
Block of four PE switches. Bipolar Hall effect devices sense the movement of a small section of flexible magnet
attached to the aluminium risers, which sit on top of neoprene rubber diaphragms.
Travel is less than 1 mm. |
Adjusting. Switches are fed a pneumatic signal from the motorised 'air pulser' on the right.
The output from a Hall effect device is monitored with a digital oscilloscope
and the position of the Hall effect device is adjusted to achieve the correct
waveform. |
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New roll reader (2006-2011) |
Suction pump The DC motor speed depends on the position of the regulator pneumatic relative to
a Hall effect device. Any deviation from the set point (adjusted by the spring
tension on top of the pneumatic) causes the motor speed to adapt accordingly.
The suction level is adjustable between 2.5" and 3.5" WG. |
PE switch array and tubing. The 25 modules comprising 100 PE switches are mounted on a PVC baseplate and connected
to a manifold on the back of the spool box. Each group is covered by a clear
plastic cover that seals against the baseplate, and suction is applied to
the inside of each cover. |
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