Overview

Lead Institution: Shirley Ryan Ability Institute

Openings: We are no longer accepting students for this project

Funded by TATRC and CDMRP

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Latest results

Flavor of the research

The majority of existing prosthesis users rightfully want more—more speed, more torque, more degrees of freedom, etc…[1]. But only 50-70% of persons with an upper-limb amputation use a prosthetic device[2]. There is thus a substantial white-space that could be filled if the needs of this untapped ground of end-users could be filled. However, the needs of this group are very different, and indeed can be characterized by wanting less, not more. Specifically, persons with an amputation who reject the use of existing prostheses want less weight, in order to have better comfort, and they want less size, in order to preserve cosmesis [2]. There is a key gap in designing a lightweight prosthesis that enables this substantial subset of the population to use prosthetic technology.

RIC has developed a lightweight, modular prosthetic arm targeted to fit the anthropomorphic weight and dimensions of a 25th percentile female. Cosmetic material and pylons can be extended to make this device appropriate is size and weight for 87% of the population. This arm has been achieved through looking closely at the engineering requirements of key design features, in light of the clinical realities of prosthesis use.

We have developed custom exterior-rotor motors; a type of motor that achieves high torque and efficiency compared with conventional robotic motors [3]. Particularly, this type of motor is optimal for the ballistic motions seen in prostheses [4], in which a prosthetic limb starts at rest, quickly ramps up to speed, and is at rest at the other end of its range of motion within a scarce 0.4 seconds. The huge accelerations incurred during these rapid movements, and the resulting forces caused by inertial components such as gear transmissions, have a large effect on the energy efficiency of the mechanism, and RIC has developed motors that are tuned to the daily requirements of activities of daily living.

We have also developed custom cycloid gears. Cycloid gears offer a large gear ratio, rugged design, and a compact size. If designed properly, they can achieve high gear ratios—even at low torques, where conventional gears have poor efficiency [5]. Their design can be scaled to different sizes using a framework to properly transform the geometry [6].

This project resulted in several patents [7,8], several component licenses to commercial partners, and publication of the complete arm [9].

References

[1] D. J. Atkins, D. C. Y. Heard, and W. H. Donovan, “Upper- Epidemiologic Overview of lndividuals with Upper - Limb Loss and Their Reported Research Priorities.”

[2] E. Biddiss and T. Chau (2007), “Upper-limb prosthetics: critical factors in device abandonment.,” Am. J. Phys. Med. Rehabil.

[3] J. W. Sensinger, S. D. Clark, and J. F. Schorsch (2011), “Exterior vs. Interior Rotors in Robotic Brushless Motors,” IEEE Conference on Robotics and Automation. Shanghai, China.

[4] J. W. Sensinger (2010), “Selecting motors for robots using biomimetic trajectories: optimum benchmarks, windings, and other considerations,” IEEE Conference on Robotics and Automation. Anchorage, Alaska.

[5] J. W. Sensinger (2013), “Analytical expression of the efficiency of high-sensitivity gear trains,” ASME J. Mech. Des.

[6] J. W. Sensinger (2010), “Unified approach to cycloid drive profile, stress, and efficiency optimization,” ASME J. Mech. Des..

[7]. Sensinger and Lipsey (2018), Modular and lightweight myoelectric prosthesis components and related methods. United States Patent No. 9579218B2

[8]. Sensinger and Lipsey (2018), Modular and lightweight myoelectric prosthesis components and related methods. United States Patent No. 9839534

[9]. Lenzi T, J Lipsey and J Sensinger (2016). Design of a small, anthropomorphic transhumeral prosthetic arm. IEEE Transactions on Mechatronics. DOI: 10.1109/TMECH.2016.2596104