Due to improvements in actuators and computation, applying good robot design is essential to achieve optimal performance. One source of inspiration is mimicking biology, attempting to translate muscle function and topology into actuator concepts based on the assumption that the human musculature has evolved to minimize energy consumption. This results in mono- and biarticular-compliant actuators, which have shown great potential to reduce the energy consumption of robotics. However, the challenge is to decide on actuator parameters.
We investigated using co-design for optimizing mono- and biarticular compliant actuators inspired by human musculature. Six bio-inspired compliant actuators were defined that were co-designed in four different configurations, applied to a 3-DoF leg model. The results showed that, compared with a fully actuated series-elastic actuator configuration, co-designed compliance showed a significant reduction in energy consumption of around 80\% on average, with a biarticular configuration performing best with a 90\% reduction, which is contributed to its use of energy transfer between the biarticulated joints. These results resemble what was found in literature, showing that co-design could be used as a tool for designing compliant actuation.