When a doctor taps the tendon just below the kneecap, the lower leg straightens automatically. This knee reflex is one example of how the nervous system controls movements without conscious involvement. Now researchers from Tohoku University (Japan) have made a mechanical module that reproduces such a reflex in a robot and allows it to walk on two legs. The work was published in the journal Advanced Intelligent Systems.
In conventional robots, reflexes require electronic sensors that monitor the state of artificial muscles. This complicates the design and increases the computational load and energy consumption. The Japanese team decided to abandon such a scheme: their module combines a sensitive element, "computation" and an actuator - all in a single mechanical part.
The module determines when an artificial muscle is stretched beyond a set threshold and automatically contracts it in response. The principle is inspired by muscle spindles - sensitive structures in human muscles that report the degree of stretch to the nervous system. In addition, the module's activation threshold can be adjusted.
By embedding the module in a robot with artificial muscles, the researchers reproduced the knee reflex. They then added a higher-level control system that changed the threshold depending on the phase of movement. As a result, the robot was able to walk on two legs.
The authors emphasize that the work shows that basic sensorimotor functions can be built directly into the mechanical structure rather than relying entirely on electronic control. In the future, this could reduce the complexity, computational requirements and energy consumption of such robots. However, for now this is a laboratory prototype, not a finished product.
Going forward, the team plans to combine mechanical reflex modules with minimal electronics to create robots with a much larger number of artificial muscles.