Acoustic Length Sensor for Soft Extensible Pneumatic Actuators with a Frequency Characteristics Model

Ken Takaki, Yoshitaka Taguchi, Satoshi Nishikawa, Ryuma Niiyama, Yoshihiro Kawahara

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


In this study, we present a length sensor that can be used for extensible soft pneumatic actuators. Conventional length sensors detect the changes in electrical resistance and capacitance owing to the deformation of the actuator; hence, deterioration and destruction occur when they are used with an actuator that has a large expansion ratio. In addition, their low resolution and linearity makes them unsuitable for use in actuator control. Our proposed sensor comprises only a speaker and a microphone installed at one end of the actuator. We propose a method to deterministically measure the length of a tube by generating a broadband acoustic signal in a tube and measuring the resonance characteristics determined by the shape of the tube. Our experimental results demonstrate that the error in the measurement with our sensor is not more than 4% with a strain up to 200%. Unlike conventional acoustic sensing methods that measure the time of flight by using ultrasound, our proposed method yields accurate results even when the tube is bent. Therefore, the proposed method can be applied to various types of pneumatic actuators.

Original languageEnglish
Article number8772162
Pages (from-to)4292-4297
Number of pages6
JournalIEEE Robotics and Automation Letters
Issue number4
Publication statusPublished - Oct 2019
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Control and Systems Engineering
  • Biomedical Engineering
  • Human-Computer Interaction
  • Mechanical Engineering
  • Computer Vision and Pattern Recognition
  • Computer Science Applications
  • Control and Optimization
  • Artificial Intelligence


Dive into the research topics of 'Acoustic Length Sensor for Soft Extensible Pneumatic Actuators with a Frequency Characteristics Model'. Together they form a unique fingerprint.

Cite this