The picture below shows the heart of the folding mechanism. The paper is fed under the narrow white platform by the first and second rollers. When it reaches the centre of the machine, it stops and is folded up around the platform by a pair of flaps which rise up on either side, first one side and then the other. Paper movement then resumes, with the centre roller feeding the folded paper off the end of the platform and into the creasing rollers.

Supporting the folding platform was tricky, because it needs to be free of obstructions above, below and on three sides. The only place it can be supported is from above at the input end, and you can see it pivoting on the shaft with the spring clips. You can also see one of the rubber bands that supplies tension to press the platform down onto the centre roller. The design is a compromise between applying enough pressure for the paper not to slip, and not applying so much pressure that the platform bends, because it must be kept thin to achieve a good fold.

The small rectangular gap in the platform is the hole for an optical sensor which detects when the paper has reached the correct position for folding.

Click on the pictures at right for some more views of the folding mechanism.

Flaps up

Flaps from underneath

Flap drive motors