Fig. 12
Stiffness of each actuator when the sensing failures were intentionally caused: the vertical axis depicts the unbounded version of \(k_i\), which can be encoded by sigmoid function; during the sensing failures, the FB policy outputted obviously erroneous stiffness; in contrast, the FF policy could hold the periodic outputs; note that the phase and amplitude deviations in the area without the sensing failures can be attributed to incomplete skill transfer and recovery attempts from lateral deviation