Evaluation of a body-powered prehensor - Rehabilitation Institute of Chicago

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Evaluation of a Novel Body-Powered Prehensor

Project Overview

Project R1

Ashley Swartz, a research engineer at the Center
for Bionic Medicine, explains how RIC's novel
VO/VC prehensor works.

Objective: To evaluate the clinical utility of a voluntary open (VO)/voluntary close (VC) prehensor, or split-hook grasping device.

Watch a video of the prehensor in action here.


Despite a cultural fascination with robotic prostheses, many amputees still prefer using body-powered prostheses, in which users move their shoulder to operate the device.

Body-powered prehensors (split-hooks and other non-anthropomorphically shaped terminal devices) are considered more functional than body-powered hands, as they are durable and simple to manipulate.

  • VO/VC device in voluntary open (VO) state.
  • VO/VC device in voluntary close (VC) state.

Currently, however, users must choose between two types of prehensors: voluntary open (VO) devices, in which the user exerts force to open the device; and voluntary close (VC) devices, in which the user actively closes the device.

VO devices provide a weak grasp force of only a few pounds, but are easy to use. VC devices enable the user to apply large grasp forces but require the user to constantly exert force to hold an object.

With previous funding from the National Institute on Disability and Rehabilitation Research (NIDRR), we have developed a prehensor with an innovative yet simple manual switching system that enables a user to operate the device in either VO or VC mode. This VO/VC device can be used in the VO mode for manipulating light objects, and can easily be switched to VC mode to provide a high grasp force, when needed.

We plan to evaluate this device's clinical viability by objectively quantifying how amputees use these devices in their home environments.

Target Population

Persons with upper-limb amputations. This population comprises many thousands of people in the United States, including many combat-injured military service personnel, who are overwhelmingly young and active.

A working model of the VO/VC prehensor.

A working model of the VO/VC prehensor. Left: Parts of the VO/VC prehensor. Middle: The VO/VC uses industry-standard fingers (tongs). Right: The VO/VC in cable-relaxed and cable-pulled positions.

Resources & Statistics



Amputee Coalition

UnLIMBited Potential (RIC Support Group)

RIC Life Center


K. Ziegler-Graham, et al., "Estimating the prevalence of limb loss in the United States: 2005 to 2050," Archives of Physical Medicine and Rehabilitation, vol. 89, pp. 422-429, Mar 2008.

Berning, Kelsey, et al. "Comparison of body-powered voluntary opening and voluntary closing prehensor for activities of daily life," Journal of Rehabilitation Research & Development. 51.2 (2014).



We will update this page periodically with project news and related interviews.


Sensinger JW, Lipsey J, Thomas A, Turner K. "Design and evaluation of voluntary opening and voluntary closing prosthetic terminal device." Journal of rehabilitation research and development 52.1 (2015): 63.

Video Interview with Research Engineer Ashley Swartz

Sensinger J, Lipsey J, Thomas A, “VOVC Body-powered hand with multiple grasp patterns” International Society of Prosthetists and Orthotists June 22-25, 2015, Lyon, France


YouTube Video of Prehensor in Action

Sensinger, J.  Initial Experience with the RIC VO/VC terminal device. Myoelectric Control Symposium (MEC), Fredericton, New Brunswick, August 18-22, 2014.

"Voluntary-Opening/Voluntary-Closing Body-Powered Terminal Device Provides New Level of Functionality" (2014 RESNA Conference Presentation)

Project Staff

RIC's Todd KuikenTodd A. Kuiken, MD, PhD, Principal Investigator. Dr. Kuiken is director of the Center for Bionic Medicine (CBM) within the Rehabilitation Institute of Chicago. At CBM, Dr. Kuiken leads an interdisciplinary team that includes physicians, prosthetists, therapists, neuroscientists, engineers, software developers, graduate students, and post-doctoral researchers. He received his BS in biomedical engineering from Duke University, and his MD and PhD degrees from Northwestern University.

Arun Jayaraman, PT PhD

Arun Jayaraman, PT, PhD, Co-Investigator. Dr. Jayaraman is Director of the Max Nader Center for Rehabilitation Technologies and Outcomes Research within the Center for Bionic Medicine at the RIC. He received his doctorate in rehabilitation sciences from the University of Florida and completed his post-doctoral training at the RIC. The overarching goal of his research is to inform clinical practice through rigorous investigator-initiated and industry-sponsored outcomes research.

Jim Lipsey

Jim Lipsey, MS, PE, Engineering Project Leader. Mr. Lipsey is an engineering manager at the Center for Bionic Medicine. As engineering manager, he is responsible for long-term planning and day-to-day execution in developing complex electromechanical systems; hiring and managing team members; defining internal processes; and technical mentoring. He received his B.E. and M.S. degrees in mechanical engineering from Vanderbilt University.

Jon SensingerJon Sensinger, PhD, Collaborator. Formerly with the Center for Bionic Medicine, Dr. Sensinger is currently Associate Director of the Institute of Biomedical Engineering at the University of New Brunswick. His research interests include body-powered and robotic prosthesis design and control, with a specific interest in developing-world applications. He focuses on developing clinically relevant, low cost/weight systems. Dr. Sensinger received his PhD in biomedical engineering from Northwestern University.

Ashley ThomasAshley Swartz, BSME, Research Engineer. Ashley Swartz is a research engineer in the Prosthetic Design & Control Lab at the Center for Bionic Medicine. She specializes in the mechanical design of body-powered and myoelectric upper- and lower-limb prosthetic devices, as well as the mechanical design of body-powered and myoelectric upper- and lower-limb prosthetic devices. She received her BSME in mechanical and bioengineering from Kettering University.

Kristi TurnerKristi Turner, OTR/L. Kristi Turner is a research therapist at the Center for Bionic Medicine and also treats patients at the Rehabilitation Institute of Chicago's Outpatient Center. She is a member of the American Academy of Orthotists and Prosthetists, the International Society for Prosthetics and Orthotics, and is a contributing faculty member at Northwestern University’s Prosthetics-Orthotics Center. She specializes in the treatment of upper limb amputation, multiple limb amputations, and burn injury. Ms. Turner earned a BS degree in occupational therapy from Saginaw Valley State University.

The contents of this website were developed under a grant from the National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR grant number 90RE5014-02-00). NIDILRR is a Center within the Administration for Community Living (ACL), Department of Health and Human Services (HHS). The contents of this website do not necessarily represent the policy of NIDILRR, ACL, HHS, and you should not assume endorsement by the Federal Government.