Bionic design and assistance performance analysis of a biarticular knee-ankle exoskeleton driven by pneumatic artificial muscles

The triceps surae muscle serves as the primary power source for ankle push-off during normal walking and contributes to improved gait economy. However, insufficient power output from the muscles around the ankle joint leads to increased metabolic cost. In this study, a pneumatically driven biarticular knee-ankle exoskeleton robot was designed based on the biomechanical principles of ankle push-off, employing artificial pneumatic muscles to mimic the synergistic actuation characteristics of the soleus and gastrocnemius muscles. Using the indirect calorimetry device K5, assistance performance experiments of the exoskeleton were conducted under different walking speeds (0.2, 0.4, and 0.6 m/s), slopes (level ground, 5° uphill, and 5° downhill), and assistance parameters (low, medium, and high magnitude). The results showed that compared with walking unpowered exoskeleton, medium-intensity (2.25 bar) assistance reduced the metabolic cost by approximately 22% (2.23 ± 0.47 W kg −1 ) during walking at 0.2 m/s on level ground. During walking at 0.6 m/s on a 5° uphill slope, high-intensity (3.0 bar) assistance reduced the metabolic cost by approximately 15% (4.08 ± 1.04 W kg −1 ). The effectiveness of assistance varied significantly across terrains under the same assistance intensity. This study provides valuable insights into the exoskeleton adaptability used on diverse terrains and the bionic design of exoskeletons.