The servo arrangement will regulate itself up to maximum rating of the servo.
Reason being it is a geared down permanent magnet motor of relatively constant speed.
Usual rating is Kg/cm and for a standard rc servo the maximum applied voltage is 6.0V.
If you look you will see there is also a speed spec that is covered as long as you are within the load and voltage limits.
Meaning as you go further out on the supplied servo arm it can push (X)kg from (X) cm out from the pivot centre of the arm. Only thing that will change(minimal) is the speed of the slider as the arm motion creates and arc travel.
The speed is not important, it should be about 1 rpm, variation is accepted. For me is the constant torque throughout the process very important. It should be possible to adjust the force. For example i put a value 100 N into the programm on the laptop and the control should adjust the needed torque for the constant force.
My question: Is this possible and how can the controller can be realized?
Why don't you simply try one and see instead of getting bogged down in all this imaginary theory that will never be disproved anyhow.
At the moment i am in the planning phase and do not have the crank slider mechanism.