Fig. 4
A representative example of the FEL controller performance for user 1. a The tracking error during trial 1 (blue) and trial 12 (red) for shoulder (left) and elbow (right) joints. b The output signal (pulse width -PW-) of the feedback error learning controller during the first (upper row) and twelfth (lower row) movement execution. Feedback (red) is the control signal given by the feedback controller; Feedforward (blue) represents the control action of the feedforward controller; Total (black) corresponds to the total control signal (PW)