Traditional mechatronic systems utilize stiff actuators, but applications such as prostheses, rehabilitation exoskeletons, legged robots, and industrial robotics have begun to integrate variable-compliance mechanisms into their systems. Several variable-compliance mechanisms have been designed and tested, but they tend to have low ranges of stiffness and complex designs. A variable-compliance system known as the Adjustable Mechanism with a Nominally Infinite Range of Stiffness (AMNIRS) has been previously designed and tested. The AMNIRS device can theoretically achieve stiffnesses from zero to rigid.

Through this work, a continuation of the AMNIRS device, AMNIRS-II, has been developed and tested. AMNIRS-II is an improved design that addresses several design limitations in the original AMNIRS device. In addition, AMNIRS-II is smaller than the original AMNIRS, and therefore provides an anthropomorphic configuration. AMNIRS-II was developed in two stages:​ miniaturization and characterization. The miniaturization phase of the project adapted the original AMNIRS design into a compact device that emulated the physical characteristics of a human elbow. A prototype for the AMNIRS-II was built and characterized. The characterization phase quantified key attributes of the AMNIRS-II system. The AMNIRS-II device included an integrated stiffness setting motor. The parameters that were characterized included the rotational stiffness, elastic energy storage, and stiffnessvarying capabilities. The results of the characterization verified the desired characteristics of AMNIRS-II. AMNIRS-II is a compact device that may be integrated into a prosthetic forearm in future work.