What i meant was something else, for a cartesian bot which completes a layer / slice, by moving X and Y together. Then the Z is used, but in separate movements, distinct from x and y, because Z is just sort of a layer change. I believe this is commonly called 2.5D in a generic machine. We use an extruder for toolhead, that adds up as a full dimension because it is used together with x and y. But in our case, for printers, we still use Z separate. We print a slice, then move to the next one, this is how it works. We do not print with movements which include Z. So this is x+y+e counting as 1 each, and with Z like that we have somewhat of a 3.5D space. To have full 4D, we would have to deposit plastic in Z direction, that is in a diagonal move across multiple layers, but we do not do that.
In a delta you could use the 3 closed loops for the 3 motors and then you will have to use z and also extruder in open loop. It still would work a bit better if there were 4 closed loops to include extruder. Also on a separate note, the resolution and closed loop are different concepts and not related. Also you would not have to use the closed loop, its not something mandatory but optional. Or better yet, this is rather a sort of a wishlist feature, since no reprap has that now. Currently reprap drivers are open loop.
In a delta you could use the 3 closed loops for the 3 motors and then you will have to use z and also extruder in open loop. It still would work a bit better if there were 4 closed loops to include extruder. Also on a separate note, the resolution and closed loop are different concepts and not related. Also you would not have to use the closed loop, its not something mandatory but optional. Or better yet, this is rather a sort of a wishlist feature, since no reprap has that now. Currently reprap drivers are open loop.