How to write this function formula ??

I have a pantograph object already break to 5 piece, i want to animate it like in shinkansen E5 by ginga that we can raise/lower using number 7.

I dont want to just copy and paste his function, i want to learn how it works so i try it and i found this simple formula:

TranslateYDirection = 0,1,0
TranslateYFunction = if[pluginstates[10] < 1, 0.8, 0]

But it just move the object to 0.8 meter higher instantly, not moving the object slowly like in his addon.

How to move it slowly until it reach the position i set it ?

TLDR
I want the object moving to next position when i press the key and if the object already in the next position it should back to original position when i press the key again.


Note: if i already understand how it works im gonna make some preset formula and release it to public domain so anyone can use that formula as freely as possible.