Cooperative antagonistic mechanism driven by bidirectional pneumatic artificial muscles for soft robotic joints

Actuators and mechanisms are the most important components of soft robots. In this study, we introduce a novel actuator capable of bidirectional force transmission, and an antagonistic structural pair mechanism that can cooperate with actuators. A tendon that runs through the interior of the actuator allows bidirectional force transmission. Each contraction and expansion can produce 124.46 N and 122.80 N of force, and maximum contraction and expansion ratios of 75.1% and 402.1%, respectively. However, a cooperative antagonistic mechanism that can transmit force in the pushing direction using a soft frame and a closed-loop tendon has also been developed. Remarkably, it exhibits 2.58 times the lumped torque density compared to a traditional antagonistic mechanism. When integrated into a robotic arm, this mechanism enables the arm to lift a 2 kg object by 117° on a 30 cm moment arm. The robotic arm itself is efficiently designed, with a 340 mm upper arm and a 300 mm forearm, maintaining a lightweight structure at just 380 g.