Airbus58
This summing point or "Differential Mechanism" is an interesting unit whose net output is via a push pull rod that exits out of the stab compartment and travels up the rear spar face of the fin. Vertical motion from the differential mechanism is converted into horizontal motion through a bellcrank, one for each of the 3 rudder PCU's. Another rod from the bellcrank attaches to the PCU spool valve, movement of which ports hyd fluid to the head or rod side of the actuator.
Rudder travel limitation is simply done by restricting the vertical travel of the push pull rod on the backside of the fin thereby limiting PCU input.
To get back to the differential mechanism, it can receive simultaneously mechanical rudder peddle input(cable loop) and yaw damp actuator input (through the rudder peddle transducer -> FAC). In manual flight it is constantly balancing out these two inputs finding a null point resulting in the net push pull rod output as mentioned above.
There is a little bit more involved of course, but I think this cuts to the chase.
N2