This paper introduces a distributed variable impedance actuator that provides independent control of the actuator's angular position and its impedance. The idea for the actuator was inspired by the morphological structure of muscles and tendons. The system to be presented can be used as both a variable impedance actuator as well as a passive piecewise linear spring. Moreover, the actuator has an adequate number of degrees-of-freedom to approximate any nonlinear spring characteristics because of its distributed nature. Using distributed torque production subsystems with small and low power motors makes it possible to use this actuator in many applications such as prosthesis, artificial limbs, and wearable robots. The stability of the system discussed and the conditions that ensure the system stability are presented. Finally, a proof-of-concept actuator design is presented, as well as experimental results which confirm that the proposed distributed variable impedance actuator can be implemented in practical applications.

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