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Twisted Rubber Variable-Stiffness Artificial Muscles.

Tim Helps1,2, Majid Taghavi1,2, Sihan Wang1

  • 1Department of Engineering Mathematics, University of Bristol, Bristol, United Kingdom.

Soft Robotics
|December 20, 2019
PubMed
Summary
This summary is machine-generated.

We developed a novel variable-stiffness artificial muscle (TRAM) using twisted rubber cord. This inexpensive and controllable TRAM technology offers significant advantages for robotics and human-robot interaction.

Keywords:
artificialmusclerubbertwistedvariable-stiffness

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Area of Science:

  • Robotics and Artificial Intelligence
  • Materials Science

Background:

  • Variable-stiffness artificial muscles are crucial for advanced robotic applications like locomotion and human-robot interaction.
  • Existing technologies (pneumatic muscles, jamming, series elastic actuators, shape memory polymers) face limitations in cost, complexity, power requirements, or control.

Purpose of the Study:

  • To introduce a new, cost-effective, and controllable variable-stiffness artificial muscle concept: the twisted rubber artificial muscle (TRAM).
  • To investigate the mechanical properties and control capabilities of TRAMs made from twisted rubber cord.

Main Methods:

  • Investigated the behavior of four rubber cord types under varying twist angles.
  • Evaluated stiffness reduction and tensile force modulation.
  • Demonstrated simultaneous control of system equilibrium position and natural frequency with a single TRAM, and independent position and stiffness control using an antagonistic TRAM pair in a robotic arm.

Main Results:

  • Identified fluoroelastomer (FKM standard) rubber for the greatest reversible average stiffness reduction (56.42%) and silicone rubber for the greatest initial stiffness reduction (92.62%).
  • Showcased that tensile force and stiffness are controllable by adjusting twist angle, with nonlinear buckling behavior occurring beyond a threshold angle.
  • Successfully demonstrated simultaneous and independent control of position and stiffness in robotic systems.

Conclusions:

  • The twisted rubber artificial muscle (TRAM) offers a simple, inexpensive, and controllable solution for variable-stiffness actuation.
  • TRAMs overcome limitations of previous artificial muscle technologies.
  • TRAMs are suitable for immediate integration into diverse robotic systems.