Thanks for your answer.
I need the axis rotating in only one direction because we need too much precision in the position of the axis, I explain it better:
We are working with Mx Automation (an interface to program the robot on a PLC), so in order to improve the precision on the axis position we have installed an encoder with an inductive sensor to count each flank when the axis is on the 'cero' position. When we rotate in one direction the flanks are precise but if we change the direction (the operator in manual or the automatic program in any movement) the flank will be executed in the other side of the inductive sensor, introducing an error in the position.