Siqi Li∗ and Chunlu Wang∗∗
SEA, interaction stability, force control, LMI, passive index
Series elastic actuator (SEA) robots combine the precision of force control with the safety of physical contact. However, the interaction stability needs to be considered in force control design. This article proposes a linear matrix inequality (LMI) on the basis of the concept of a passive index to solve the problem of the force control design of SEAs. First, the interaction behaviour is modelled as an impedance– admittance feedback interconnect system. Second, the stability conditions of the interaction process are analysed by input–output stability and (Q, S, R)-dissipation theory. Then, the passive index relationship of a subsystem is analysed when the interaction system between the robot and the environment is passive. An interaction stability condition based on the passive index is proposed, and an LMI with the passive index is derived. An LMI method is used to solve the multi-objective synthesis problem by satisfying both the passive index and force tracking. Simulation results show that the SEA force controller designed by this method can not only adjust the passive index according to the interaction environment to meet the interaction stability condition but also accurately realize force tracking.
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