Li Monica S, Stuart Hannah S
Department of Mechanical Engineering, University of California Berkeley, Berkeley, California, USA.
School of Engineering & Applied Science, Yale University, New Haven, Connecticut, USA.
Soft Robot. 2025 Feb;12(1):109-123. doi: 10.1089/soro.2023.0082. Epub 2024 Aug 2.
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 40 kHz. 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 endcaps. The compliant cap vibrates with the resonant pressure waves and is a nonidealized boundary condition, initially producing a nonmonotonic force response. We characterize two solutions-adding a distal hole and mass to the cap-resulting in monotonic and nonhysteretic force readings with this technology. We can tune each AcousTac taxel to specific force and frequency ranges, based on geometric parameters including tube length, 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. Simple to implement with off-the-shelf parts, 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.
声音是一种通过空气传播的丰富信息媒介；人们通过言语进行交流，甚至可以通过敲击和倾听来辨别材料。为了捕捉人类听力范围内的频率，商用麦克风的采样率通常超过40kHz。这些易于获取的声学技术尚未被广泛用于明确地赋予机器人触觉的目的。一些研究人员已经利用声音来感知触觉信息，既监测周围的声景，也使用嵌入式扬声器和麦克风来测量结构内部的声音。然而，这些方法通常不能直接测量稳态力，或者需要在接触位置附近集成电子设备。在这项工作中，我们展示了AcousTac，一种用于无电子设备、力敏感软皮肤的声学触觉传感器。柔顺的硅胶帽和塑料管构成了共振腔，共振腔发出由气动驱动的声音，可由传统的外置麦克风测量。由此产生的频率变化取决于柔顺端盖上的外部负载。柔顺帽随着共振压力波振动，是一种非理想化的边界条件，最初会产生非单调的力响应。我们描述了两种解决方案——在帽上添加一个远端孔和质量块——从而使用该技术获得单调且无滞后的力读数。基于包括管长在内的几何参数，我们可以将每个AcousTac像素调整到特定的力和频率范围，从而在阵列中同时唯一地感知每个像素。我们在两个机器人系统上展示了AcousTac的功能：一个4像素阵列和一个3像素收缩式夹具。AcousTac使用现成的部件易于实现，对于软机器人表面的力传感来说是一个很有前景的概念，特别是在接触位置附近的电子设备不合适的情况下。为机器人配备触觉传感和软皮肤，能赋予它们触觉以及与周围环境安全交互的能力。
