Transforming Insect Electromyograms into Pneumatic Muscle Control

Biological inspiration has a history of advancing the field of robotics. Increasingly, robots are also being used in the modeling of biological systems. In this paper, we use recorded cockroach electromyograms (EMGs) to drive artificial muscle (braided pneumatic actuator) activation and thereby robot joint motion, in an effort to model the transformation from EMG to behavior in the animal. A muscle activation model was developed that transforms EMGs recorded from behaving cockroaches into appropriate commands for the robot. The transform is implemented by multiplying the EMG by an input gain thus generating an input pressure signal, which is used to drive a one-way closed-loop pressure controller. The actuator then can be modeled as a capacitance with input rectification. The actuator exhaust valve is given a leak rate, making the transform a leaky integrator for air pressure, which drives the output force of the actuator. We find parameters of this transform by minimizing the difference between the robot motion produced and that observed in the cockroach. Results from evaluation on reduced-amplitude cockroach angle data strongly suggest that braided pneumatic actuators can be used as part of a physical model of a biological system.