Sound is a rich information medium that transmits through air; people communicate through speech and can even discern material through tapping and listening. To capture frequencies in the human hearing range, commercial microphones typically have a sampling rate of over 40kHz. These accessible acoustic technologies are not yet widely adopted for the explicit purpose of giving robots a sense of touch. Some researchers have used sound to sense tactile information, both monitoring ambient soundscape and with embedded speakers and microphones to measure sounds within structures. However, these options commonly do not provide a direct measure of steady state force, or require electronics integrated somewhere near the contact location. In this work, we present AcousTac, an acoustic tactile sensor for electronics-free force sensitive soft skin. Compliant silicone caps and plastic tubes compose the resonant chambers that emit pneumatic-driven sound measurable with a conventional off-board microphone. The resulting frequency changes depend on the external loads on the compliant end caps. We can tune each AcousTac taxel to specific force and frequency ranges, based on geometric parameters, including tube length and end-cap geometry and thus uniquely sense each taxel simultaneously in an array. We demonstrate AcousTac's functionality on two robotic systems: a 4-taxel array and a 3-taxel astrictive gripper. AcousTac is a promising concept for force sensing on soft robotic surfaces, especially in situations where electronics near the contact are not suitable. Equipping robots with tactile sensing and soft skin provides them with a sense of touch and the ability to safely interact with their surroundings.

翻译：声音是一种通过空气传播的丰富信息媒介；人们可通过言语交流，甚至能通过敲击与聆听来辨识材质。用于捕捉人耳可听频率的商业麦克风通常具有超过40kHz的采样率。这些易获取的声学技术尚未被广泛用于赋予机器人触觉这一明确目的。已有研究者利用声音感知触觉信息，既包括监测环境声景，也包括通过嵌入式扬声器和麦克风测量结构内部的声音。然而，这些方案通常无法直接测量稳态力，或要求在触点附近集成电子元件。本文提出AcousTac——一种用于无电子力敏感软体皮肤的声学触觉传感器。由柔性硅胶帽与塑料管构成的谐振腔可产生气动驱动声音，并通过传统板载麦克风测量。所产生频率的变化取决于柔性端盖承受的外部载荷。通过调整几何参数（包括管长与端盖几何形状），我们可调节每个AcousTac触觉单元至特定的力与频率范围，从而在阵列中同时唯一感知每个单元。我们在两个机器人系统上展示了AcousTac的功能：一个4触觉单元阵列和一个3触觉单元夹持器。AcousTac为软体机器人表面力的传感提供了有前景的概念，尤其适用于触点附近不适宜集成电子元件的情况。为机器人配备触觉传感与软体皮肤，可赋予其触觉感知能力及与周围环境安全交互的能力。