Recent development of series elastic actuators have revealed a capability to mimic muscle-like properties and achieve accurate force control. Series elastic actuators have also been widely used in humanoid and surgical robotic devices. The design of the elastic elements are critical and complex. This tends to increase costs and complexity of designing and controlling series elastic actuators. Here, we present a novel low cost and easy-to-fabricate design for a series elastic element that also has adjustable stiffness. The design consists of simple shaft couplers and spring steel plates. During the test, the stiffness of the designed elastic elements is very close to linear (R2 = 0.999) when the clamped spring-steel strip length is sufficiently long. As the clamped strip length shortens, the resulting torque deflection curve becomes slightly quadratic but remains largely linear. Also, the designed elastic element exhibits little hysteresis during loading and unloading. The stiffness of the designed elastic element can be tuned to achieve a range of stiffness values, thus it is suitable for different applications with different stiffness requirements. We also design a simple control algorithm and develop a simulation based on the dynamic properties of the designed elastic element. In simulation, the controller is able to accurately track the commanded torque values. Overall, this design could help reduce the cost and development time required for series elastic actuators.

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