Acoustic Sensing for Soft Pneumatic Actuators

We propose a novel sensing method for soft pneumatic actuators. The method uses a single microphone, embedded into the actuator's air chamber. Contact with the environment induces sound (vibration) in the actuator. The materials and the shape of the actuator reflect, refract, and attenuate the sound as it propagates inside the actuator. This produces a unique sound signature for different types of events, enabling the sensing of contact locations, contact force, and the type of contacted material. Sensing is insensitive to the inflation state of the actuator and to background noise. We demonstrate the robustness and versatility of the microphone-based sensor solution in experiments with a PneuFlex actuator. The proposed sensorization avoids the fundamental challenges of sensorizing soft pneumatic actuators, because the placement of a microphone does not negatively affect the compliance of the actuator and because a single microphone suffices for sensorization of the entire actuator, eliminating the need for an application-specific sensor layout.