Blue clutch (on the left) linearly reciprocates (its motion source is not shown). It makes pink clutch (on the right) move in opposite direction thanks to the cable drive.
Both clutches make orange toothed bar move to the left when they move to the left. Thus the bar move continuously to the left.
So this mechanism converts reciprocating linear motion into continuous oneway one.
Red springs always force the knives (in green and yellow) towards the bar.
The mechanism can work even in case the bar is not toothed thanks to the friction.