Machine Electronics; Speed/Needle Position Sensor - Janome QMP16SU Manual

7. Machine Electronics

Speed/Needle Position Sensor

The main shaft speed and needle position
sensor disk mounts to the main shaft near
the back hand wheel. It comprises a disk with
two encoder regions. The outermost region
consists of 100 small segments to provide speed
feedback to the control system. The inner region
consists of only two segments: an on region and
an off region. These two regions are used for
needle positioning.
There is a forked circuit board containing an
emitter and a receiver for each of the two
encoder regions. With the front cover open and
the power and control cables hooked up and
powered on, you can rotate the hand wheel and
see the green LEDs flash to indicate that the
encoder is working properly.
The green Speed LED on the left side of the
board should flash on and off at a rate of 100
flashes per revolution as you rotate the hand
wheel. The green Needle LED on the right
should turn on to indicate the needle is in the
Up position (the take-up lever is in its highest
position) and turn off to indicate the needle is in
the Down position.
Careful inspection of these LEDs as you rotate
the hand wheel with the power on will tell you
whether the encoder is functioning properly.
Damage to the encoder disk or any build-up
of dust, oil or other material can impede the
transfer of light through the transparent portion
of the disk and cause the encoder to miss some
pulses.
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Needle Up
Needle Down