See Hydro Muscle page for more recent updates

Hydro Artificial Muscle (HAM) Exo-Musculature
Daniil Effraimidis, Brian Jennings, Gregory McCarthy, Nicholas Corso
Primary Advisor: Marko Popovic (PH/RBE/BME), Co-advisor: Cagdas Onal (ME/RBE)
2013/14 Robotics Engineering (RBE) 2nd place, Provost's MQP Award Runner up

In the news: MOVIE from Cambridge Science Festival 2014
HAM team at CSF'14.
Popovic group CSF14.

"...As research in robotics continues to progress, actuators which are lightweight, small, efficient, fluid, fast, and cost-effective become more and more critical. HAM is a simple novel actuator that confronts these requirements. It elongates when fluid is pressurized and contracts when fluid (e.g. water) is released. It may be utilized as a building block for an Exo-Musculature that can be rapidly assembled and utilized as either perform-alone or wearable, human body-symbiotic robotic system. There are many attractive avenues for future work, development, and applications for this technology. For example, it can have applications in the medical field as a device to assist in rehabilitation and physical therapy, it can be used in both labor and the military as method of augmenting strength, and it can be used as a soft-robotics alternative to virtually all rigid robotic motors and actuators that currently exist. Further research and development can advance this device from a proof of concept to one of the most commercially-feasible soft robotics actuators. ..."

2013 and before

ExoMusculature embedded in shoulder brace. Teleoperation with weight lifting (December 2011).
[click on image to see movie]
ExoMusculature embedded in shoulder brace. Teleoperation with time delays (December 2011).
[click on image to see movie]
Naked ExoMusculature.
Teleoperation with weight lifting (December 2011).
[click on image to see movie]

Exomusculature concept (and soft robotics in general) is about moving away from an old paradigm, i.e. robotics with only rigid joints and links, toward novel ("softer") architectures, materials, actuations, sensing and control and perhaps with all of those more biologically inspired. It is of less importance whether actuation is based on ordinary cable, EAP, PAM (McKibben), or something else. What matters is that it is practical.


We introduced the word Exo-Musculature in March 2012 to describe a compliant, thin, light-weight, self-actuated multi-component garment without singular joints or rigid elements; hence very different concept than the traditional Exo-Skeleton. Exo-Musculature takes advantage of natural anatomical structures, including joints and bones, to provide the device structure and maintain the natural kinematic degrees of freedom (DoF). Additionally, the adaptive control identifies linear and angular misalignment parameters of the exomusculature relative to the wearer and self-compensates for optimal actuation.This work builds upon the Soft Robotics Shoulder Brace project (WPI Popovic Labs in collaboration with Robert Howe's Harvard Biorobotics Lab).

One of the problems of biologically realistic Exo-Musculature is its portability. For the human body, there are about 400 pairs of skeletal muscles, each of which is composed of one hundred or more individual motor units. Each motor unit represents a single independently actuated DoF. Hence, if an exo-musculature is to mimic just one percent of human musculature, the number of actuated DoF has to be on the order of one thousand. However, conventional approaches involving one dedicated electric motor per actuated DoF result in systems that are very large, heavy, and expensive. This is clearly inappropriate for a fully mobile, wearable exo-musculature. Unfortunately, this problem cannot be solved with pneumatic driven ExoMusculatures due to small energy density.

We show that OTM concept (linear OTM and rotary OTM) can be beneficial for systems like ExoMusculature that, if biologically realistic, necessitate a very large number of actuated DoFs. The practical system can be made very compact, light weight, low input - high output power, energy efficient, and finally cost-effective. The Exo-Musculature added with OTM concept is particularly applicable to biomedical applications (e.g. post-stroke rehabilitation), space robotics (e.g. by providing active garments to astronauts in order to prevent zero-gravity muscular degeneration), haptic feedback system (e.g. for 3D Internet and/or various entertainment systems), light weight robotics systems etc.

Publications and Presentations:

1. M.B. Popovic, C. Onal, G. McCarthy, N. Corso, D. Effraimidis, and B. Jennings (Publication date 2015/12/17) “Actuators and Methods of Use” (Hydro Artificial Muscles). United States Patent and Trademark Office, Assignee Worcester Polytechnic Institute. Serial No.: 62/011,830. Filed: June 13, 2014. US Patent 20,150,359,698, 2015

2. G. McCarthy, D. Effraimidis, B. Jennings, N. Corso, C. D. Onal, and M. B. Popovic (2014). "Hydraulically Actuated Muscle (HAM) Exo-Musculature" in "Robot Makers: The future of digital rapid design and fabrication of robots" (RoMa) Workshop, the 2014 Robotics: Science and Systems Conference (RSS) July 12, 2014 Berkeley, USA.

3. I. Galiana, F. L. Hammond, R. D. Howe and M. B. Popovic (2012). "Wearable Soft Robotic Device for Post-Stroke Shoulder Rehabilitation: Identifying Misalignments" 2012 IEEE/RSJ International Conference on Intelligent Robots and Systems, October 7-12, 2012. Vilamoura, Algarve, Portugal.

4. Christopher J. Berthelette, Adam L. Blumenau, Alec A. Ishak, Thane R. Hunt, (faculty) Germano S. Iannacchione, (faculty) Stephan Koehler, and (faculty, advisor) Marko B. Popovic, "Touch Tomorrow with Soft Robotics Exo-Musculature and One-To-Many (OTM) system", Poster and Demo, WPI Touch Tomorrow and the NASA Sample Return Robot Centennial Challenge, Worcester Polytechnic Institute, June 16, 2012.

(link to updated poster with all researchers pictured)

5. T. R. Hunt, C. J. Berthelette, G. S. Iannacchione, S. Koehler, and M. B. Popovic, "Soft Robotics Variable Stiffness Exo-Musculature, One-To-Many Concept, and Advanced Clutches", IEEE ICRA 2012 WORKSHOP: Variable Stiffness Actuators moving the Robots of Tomorrow, St. Paul, Minnesota, May 14, 2012.

6. C. J. Berthelette, G. S. Iannacchione, S. Koehler, and M. B. Popovic, "The One-To-Many Concept and Soft Robotics ExoMusculature" (submitted to IROS on March 10,2012)

7. Girardo, D. O., and Popovic, M. B, (2011) "Physics applied to poststroke rehabilitation; Shoulder Soft Robotics Brace", AIP SPS award December 2011 final report.

8. Blumenau, A., Girardo, D., O., Lin, E., L., Mandala, S., and Popovic, M. B, "Physics applied to post-stroke rehabilitation" ,AIP SPS award June 2011 interim report.

9. S. B. Kesner, L. Jentoft, F. L. Hammond, R. D. Howe and M. B. Popovic (2011). "Design Considerations for an Active Soft Orthotic System for Shoulder Rehabilitation" 33rd Annual International IEEE EMBS Conference, August 30 - September 02, 2011, Boston, USA.

Current Researchers:

Marko B. Popovic

Past Researchers:

Christopher J. Berthelette, Adam Blumenau, Eben C. Cobb, Nicholas Corso, Peter Dilworth, Matthew DiPinto, Daniil Effraimidis, Ignacio Galiana, David Orion Girardo, Frank L. Hammond, Rob D. Howe, Francis Hoy, Thane R. Hunt, Germano S. Iannacchione, Brian Jennings, Leif Jentoft, Samuel B. Kesner, Stephan Koehler, Gregory McCarthy, Cagdas Onal, J.D. Sareault, Ephedyn L. Lin, Sahit Mandala