Closed loop or linear scales? Or both?

Hi,

i am currently laying out my next machine and thinking about wether to go with linear scales or closed loop steppers. As I see, it does not make sense to use both, or am I missing the advantage?

your missing the advantage. steppers with encoders close part of the loop but the only way to close the entire loop is to have duel loop feedback with linear encoders on the load side as well. the encoder on the stepper closes the velocity loop and the linear encoder on the load side closes the position part of the loop.

the encoder on the stepper only keeps track of what the motor is doing in a nut shell and if you have things like backlash or any other type of mechanical error the steppers have no way of knowing. with the encoder on the load side you can correct the error because the system then knows how far things are off.

so using both is what you need for a duel loop feedback system. which is far better than a single loop if accuracy is needed to that degree.