  To eliminate the static error, overshoot, and vibration of the series elastic
actuator (SEA) position control, the resonance ratio control (RRC) algorithm is
improved based on L1 adaptive control(L1AC)method. Based on the analysis of the
factors affecting the control performance of SEA, the algorithm schema is
proposed, the stability is proved, and the main control parameters are
analyzed. The algorithm schema is further improved with gravity compensation,
and the predicted error and reference error is reduced to guarantee transient
performance. Finally, the effectiveness of the algorithm is validated by
simulation and platform experiments. The simulation and experiment results show
that the algorithm has good adaptability, can improve transient control
performance, and can handle effectively the static error, overshoot, and
vibration. In addition, when a link-side collision occurs, the algorithm
automatically reduces the link speed and limits the motor current, thus
protecting the humans and SEA itself, due to the low pass filter
characterization of L1AC to disturbance.
