Patella-Inspired Linkage Joint: Power Amplifier for Pneumatic Artificial Muscles

Pneumatic artificial muscles (PAMs) have shown promising potential as actuators for safe human–robot interaction due to their high force density and inherent compliance. However, drawbacks such as force reduction, relatively poor control performance, and low energy efficiency have hindered the practical application of PAMs for robotic systems. Although various approaches were conducted to enhance the applicability of PAMs, there is still a lack of research on effective transmission mechanisms that can fully exploit the actuation characteristics of PAMs. In this article, we propose a patella-inspired linkage joint (PatLink) to address the tradeoff problem between torque and speed in conventional mechanisms with PAMs. The proposed mechanism amplifies the joint rotation angle with respect to the muscle contraction length, thereby increasing the joint angular velocity. Furthermore, the PatLink enables the PAMs’ actuation force to be utilized over a wider range of joint angles, further improving the torque output. Experimental results showed 103% increase in range of motion and 106% enhancement in mean work rate under the same input, thereby validating the effectiveness of the PatLink. The proposed mechanism can be further expanded to various contraction-type soft actuators, such as shape memory alloy actuators and twisted string actuators, which possess similar force characteristics to PAMs.