Variable compliance has been a growing topic of interest in legged robotics due to recent studies showing that animals adjust their leg and joint stiffness to adjust their natural dynamics and to accommodate changes in their environment. However, existing designs add significant weight, size, and complexity. Series Elastic Actuators, on the other hand, are designed with a set stiffness usually tuned for actuator performance. We propose a new concept for implementing a physical spring in series with a linear SEA using a cantilevered spring. A movable pivot is used to adjust the stiffness by changing the effective length of the cantilever. While the proposed design does not allow for variable compliance, it does retain many of the benefits of passive spring elements such as absorbing impacts, storing energy, and enabling force control. The primary advantage of the design is the ability to adjust the stiffness of each joint individually without the increased weight and complexity of variable stiffness designs. This paper introduces the motivation for configurable compliance, describes the proposed design concept, explains the design methods, and presents experimental data from a completed prototype.

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