Active Acoustic Contact Sensing for Soft Pneumatic Actuators

We present an active acoustic sensor that turns soft pneumatic actuators into contact sensors. The whole surface of the actuator becomes a sensor, rendering the question of where best to place a contact sensor unnecessary. At the same time, the compliance of the soft actuator remains unaffected. A small, embedded speaker emits a frequency sweep which travels through the actuator before it is recorded with an embedded microphone. The specific contact state of the actuator affects how the sound is modulated while traversing the structure. We learn to recognize these changes in the sound and map them to the corresponding contact locations. We demonstrate the method on the PneuFlex actuator. The active acoustic sensor achieves a classification rate of 93% and mean regression error of 3.7mm. It is robust against background noises and different objects. Finally, we test it on a Panda robot arm and show that it is unaffected by motor noises and other active sensors.