Characteristic Analysis and Design Optimisation of Bubble Artificial Muscles (BAMs)

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Soft Robotics requires new actuators and artificial muscles which are lighter, lower cost and more effective than current technologies. Recently developed Bubble Artificial Muscles (BAMs) are lightweight, flexible, inexpensive, pneumatic actuators with the capability of being scalable, contracting at a low pressure, and generating sufficient tension and contraction for assisting human mobility. BAMs are simply fabricated using a commercial plastic tubing with retaining rings, forming a “bubble” shape and creating a series of contractile units to attain a desired stroke. They can deliver high contraction through optimisation of actuator length and radius, or high tension by strengthening their materials to operate at high pressure. Here we present a detailed analysis of BAMs, define a model for their actuation and verify the model through a series of experiments with fabricated BAM actuators. In tests, a maximum contraction of 43.1% and a maximum stress of 0.894 MPa were achieved, corresponding to the BAM lifting a load 1,000 times its own weight (5.39 g). The BAM model was built to predict experimental performance; for example, the relationship between tension and contraction at various applied pressures, and between contraction and pressure. Characteristic analysis and design optimisation of the BAM are presented as an approach to design and manufacture the ideal “bubble” actuator at any required dimensions. A BAM orthosis is demonstrated assisting a sit-to-stand transition on a leg mechanism, constructed to match the scale of a human’s lower limb. Guidelines for further improvement of the BAM are also included.
Original languageEnglish
Number of pages14
JournalSoft Robotics
Early online date17 Jun 2020
Publication statusE-pub ahead of print - 17 Jun 2020


  • actuator
  • pneumatic
  • artificial muscle
  • wearable
  • sit-to-stand

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