HydroBone and Variable Rigidity Exoskeleton:

Load bearing element utilizing granular media compressed by application of positive fluid pressure

Variable rigidity Exoskeleton [click on image to see movie]


The HydroBone is a variable rigidity load bearing element controlled by fluid pressure. The HydroBone consists of an inner layer, latex tube filed with pressurized fluid, and an outer layer, granular media enclosed by non-stretchable sheeting. The axial compression experiments verified that HydroBone’s stiffness and critical buckling force vary with fluid pressure. In order to avoid undesirable buckling, fluid pressure has to be larger than certain minimal value depending on external load. For wearable applications rigid elements are often uncomfortable and may obstruct movements. To address both the user comfort and the necessity for load bearing rigidity several variable rigidity devices controlled in an automatic fashion were proposed, designed, and prototype tested. Based on pressure and external load axial force fluid pressure is adjusted such that critical buckling force is outside of the in advance specified force safety margin. The HydroBone automatically stiffens when load increases and softens when load decreases. The potential applications of this technology range across numerous disciplines, including wearable assistive technologies and civil engineering.

The wearable applications are illustrated with HydroBone lower limbs variable rigidity exoskeleton. In part of the second the exoskeleton can transition in finely tuned manner from fully flexible structure, allowing greater mobility, to fully rigid structure, allowing augmented load bearing capability.

Publications and Presentations:

1. Matthew Bowers, Chinmay Harmalkar, Saivimal Sridar, Corey Majeika, Christian Kaan, Germano Iannacchione, and Marko Popovic, "An approach to HydroBone and other variable stiffness structures," The 20th International Conference on Composite Structures (ICCS20) in Paris, France, 4-7 September 2017.

2. Saivimal Sridar, Corey J. Majeika, Christian Kaan, and Marko Popovic, "Design and Control of HydroBone – An approach to variable stiffness structures using Jamming of Granular Media," WPI Popovic Labs' document, September 16, 2016.
See accompanying video HERE

3. Saivimal Sridar, Corey J Majeika, Phillip Schaffer, Matthew Bowers, Seiichiro Ueda, Andrew J Barth, Jon L Sorrells, Jon T Wu, Thane R Hunt, and Marko Popovic (2016) “Hydro Muscle - a novel soft fluidic actuator,” 2016 IEEE International Conference on Robotics and Automation (ICRA), pp 4014-4021

4. Saivimal Sridar, "HydroBone and Variable Stiffness Exoskeleton with Knee Actuation," WPI Master Thesis, WPI, Worcester, Massachusetts, US, May 2016

5. Marko Popovic, Saivimal Sridar, Corey Majeika, Nicholas Deisadze, and Erika Giancarlo, “Variable Stiffness Devices and Methods of Use,” United States Patent and Trademark Office, Assignee Worcester Polytechnic Institute. Serial No.: 15/154,443. Filed: May 13, 2016

WPI Popovic Labs, Cambridge Science Festival 2017 (Science Carnival and Robot Zoo), May 4, 2017
Welcome to Popovic Labs: December 2016 Edition , March 3, 2017
WPI Popovic Labs at Cambridge Science Festival 2016 , April 20, 2016
WPI Popovic Labs, Cambridge Science Festival 2015 (Robotics Zoo), April 20, 2015

Current Researchers:

Matthew Bowers, Chinmay Harmalkar, Germano Iannacchione, and Marko B. Popovic

Past Researchers:

Nicholas Deisadze, Erika Giancarlo, Christian Kaan, Corey Majeika, and Saivimal Sridar