Anthropomorphic adaptation of a mechanically-variable, near-infinite range-of-stiffness mechanism

Abstract

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 stiffness-varying 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.