Pulling your strings

James S. Sulzer*, Michael A. Peshkin, James L. Patton

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


While performing to expectations, the proof-of-concept MARIONET, like all robotic devices, is limited by the power of its actuators and its geometry. The concept allows both moment arm manipulation and tension control to produce torque and impedance at a joint. In addition, the moment arm path can be altered to fit the application?s requirements. For instance, a linear path may be more advantageous than a rotational path. Weight and cost can be reduced by using a highly geared drive motor and further by implementing an elastic element in series with a highly geared tensioner or even completely substituting the tensioner for a passive element. When using an active tensioner, regardless of configuration, the variable control of stiffness and equilibrium position make the MARIONET act like a variable compliant series elastic actuator. As a result, it shares many of the same advantages such as low weight, low cost, and compliance. In addition, by adding remote actuation, inertia is further reduced, the effect being amplified as the number of joints increase. This concept is illustrated in detail in previous work [14]. The technology has great potential in several areas, but one growing area that should make positive use of MARIONET transmission is in neurorehabilitation training, in which a patient learns to move correctly with repetitive training that is facilitated by interactions with a robot. For example, the financial costs of recovery from injuries such as stroke are staggering, with a projected total of US$2 trillion over the next 45 years [19]. Although a sizeable fraction (9%) of that total comes from rehabilitation costs, additional cost comes from informal care such as assistance from a family member. The compliant and safe aspects of the MARIONET make it a strong candidate for home rehabilitation, which has been shown to be comparably effective in the therapy in the clinic [20]-[22]. Although home rehabilitation is more stressful for caregivers [20], a tireless home robotic system could become a part of the standard of care. Besides rehabilitation, the MARIONET concept has potential in any application where remote actuation and mechanical compliance is desired and a high torque rate of change is not required. Such a unique device that imitates the variable moment arms of muscle and tendons may be used in teleoperation, surgery, mobile robots, micromanipulation, or hazardous material handling. Whether the application is in orthoses or in bridges, the variable compliance, lightweight, and remote actuation characteristics of the MARIONET have a promising future.

Original languageEnglish (US)
Pages (from-to)70-78
Number of pages9
JournalIEEE Robotics and Automation Magazine
Issue number3
StatePublished - 2008


  • Cable
  • End effectors
  • Exotendon
  • Humans
  • Joints
  • Mechanical cables
  • Moment arm
  • Rehabilitation
  • Robots
  • Springs
  • Torque
  • Variable impedance

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering


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