Body-powered prosthesis design
VOVC TD
VOVC TD
Lead Institution: Shirley Ryan Ability Institute
Openings: We are no longer accepting students for this project
Funded by NIDRR
Cable-operated mechanisms provide a lightweight yet highly efficient coupling between the user and their environment [1]. They work very well for applications such as bicycle brakes, in which a spring holds brake-pads apart and the user applies a force, through a Bowden cable, to close them. The user intuitively knows both the position of the brake pads and feels the force applied via the cable. Such a device could be termed a voluntary-closing (VC) mechanism, because the user applies force to voluntarily close the mechanism. In voluntary-opening (VO) devices, the closed default state of the mechanism is maintained by a spring and the user applies force to open the device; clothespins are a common place example of such a mechanism. Even the human hand can be thought of as a cable-operated system, in which pairs of tendons drive each joint. The majority of individuals who have lost their upper limb through amputation, including 68% of Vietnam veterans and 38% of Operation Iraqi Freedom / Operation Enduring Freedom veterans [2], prefer a cable-operated, body-powered device over a myoelectric prosthesis (e.g., [3], [4] [5]). Body-powered devices provide improved accuracy [6] and extended physiological proprioception [7] in conjunction with rugged design [8], [9]. However, as with the bicycle brakes and clothespins described above, and unlike the intact human hand, current body-powered prostheses only use a single cable and thus only enable one degree of freedom (DOF). Body-powered prehensors are thus limited to either VO or VC mode.
Although there are advantages and disadvantages for both types of device, most body-powered prosthesis users chose VO devices. The advantage of these devices is that once the object has been grasped, the user does not need to exert force to maintain that grasp; a spring provides a grip (or pinch) force to hold the object. This allows the user to relax and not be concerned about maintaining cable tension while maneuvering their terminal device, and the object, in space. The pinch force is determined by the spring tension; for the majority of devices the spring tension is fixed, and is chosen so as to be adequate for most moderately-weighted objects used for daily tasks. However, this spring tension may be excessively strong for some tasks and not strong enough for others (e.g., holding heavy, irregularly shaped, or slippery objects). This limits what types of object the user can successfully manipulate. In addition, users must overcome the force of the spring each time they open the device, which requires unnecessary energy expenditure whenever the user only needs to hold relatively light objects. Some VO prehensors allow the user to adjust spring tension (e.g., [10], [11]) but only over a limited range of forces. In contrast, for VC devices, the pinch force is generated by the user. A benefit of this design is that the user can apply the appropriate force for every task, from small forces to large forces; thus the user need only expend the energy required for the given task. However, in most designs the user must maintain the pinch force, and hence continue to generate this force throughout the entire task, which can cause fatigue. Although some VC devices have a clutch that enables the user to relax cable tension while holding the object, the clutch must be disengaged at the end of each movement, which requires an additional action. In addition, clutches often wear out. As both VO and VC devices are useful for different subsets of tasks, having to choose one or the other type of device means that body-powered prosthesis users have difficulty being efficient over the range of tasks they are likely to encounter on a daily basis, and many desire devices that are more broadly functional [12].
Several groups have tried to design a body-powered prehensor that provides both VO and VC modes. Some have designed mechanisms in which the device transitions between modes over the course of cable excursion (e.g. [13]–[17]). These devices are easy to operate because they don’t require a switching mechanism, but they can only generate half of the pinch force of conventional devices since the tong must travel twice as far (i.e., in both the open and close directions) for a given range of cable excursion. This fundamental fact of physics seems likely to limit the clinical viability of this class of devices [16].
Two other groups have created devices that can switch between VO and VC modes and can provide the pinch-force obtained from conventional devices. However, the challenge has been to design devices that are clinically viable. Sullivan and Siong recently produced a prototype based on a gear transmission, but this design is bulky and heavy and has inefficiencies due to the gears [18]. Perhaps more importantly, the Bowden cable attachment site (commonly called the thumb in the prosthetics field) does not remain the same in the two configurations, which requires the end-user to adjust harness tension every time they switch modes in order to capture the limited cable excursion they can generate with their harness. It is more challenging to design a device in which the end-effector position remains fixed while the Bowden cable attachment changes from an open to a closed position. Veatch has accomplished such a design in a device termed LESA [19], but the implementation was again too heavy and bulky to be clinically viable. In addition, in this design either the lateral or medial tong moves, depending on the mode. In conventional prehensors, the moveable tong is always the lateral (radial) tong as this allows the user a better line-of-site to the moving tong and the object being manipulated. However, despite these acknowledged design limitations, subjects in pilot studies expressed enthusiasm over the central concept of being able to switch between modes [19].
In a recent study that supports this finding, we found that the majority of able-bodied subjects performing the Southampton Hand Assessment Procedure (SHAP) [20] with both VO and VC devices expressed a desire to switch between modes on a task-by-task basis [21]. Thus a strong need exists for a device that can switch between modes, but clinical viability requires it must be the same size and weight as conventional devices; it must maintain the same default Bowden cable attachment position in both modes; the lateral tong must be the moveable tong in both modes; and the mechanism must be simple enough to allow manufacturers to fabricate the device for a reimbursable cost.
We have designed a device that uses a linkage singularity to achieve both VO and VC mode with a simple switching mechanism. The device has gone through a series of iterations and field tests [21].
We've also developed a body-powered hand version, which includes the VO/VC switching device along with lockable fingers and a positionable thumb. The combined features enable the hand to be prepositioned in a variety of configurations while retaining the efficiency of simpler body-powered devices [22].
[1] A. Schiele, P. Letier, R. Q. Van der Linde, and F. Van der Helm, “Bowden Cable Actuator for Force-Feedback Exoskeletons,” Proceedings of the 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems. Beijing, China, pp. 3599–3604, 2006.
[2] L. V. McFarland, S. L. H. Winkler, A. W. Heinemann, M. Jones, and A. Esquenazi, “Unilateral upper-limb loss: Satisfaction and prosthetic-device use in veterans and servicemembers from Vietnam and OIF/OEF conflicts,” J. Rehabil. Res. Dev., vol. 47, no. 4, p. 299, 2010.
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[6] L. Vodovnik and S. Rebersek, “Information-Content of Myo-Control Signals for Orthotic and Prosthetic Systems,” Arch. Phys. Med. Rehabil., vol. 55, no. 2, pp. 52–56, 1974.
[7] D. C. Simpson, “The Choice of Control System for the Multimovement Prosthesis: Extended Physiological Proprioception (e.p.p),” in The Control of Upper-Extremity Prostheses and Orthoses, P. Herberts, R. Kadefors, R. Magnusson, and I. Petersen, Eds. Springfield, IL: Charles Thomas, 1974, pp. 146–150.
[8] R. F. ff. Weir and J. W. Sensinger, “Design of Artificial Arms and Hands for Prosthetic Applications,” in Biomedical Engineering and Design Handbook, 2nd ed., vol. 2, M. Kutz, Ed. New York: McGraw-Hill, 2009, pp. 537–598.
[9] C. M. Fryer, G. E. Stark, and J. W. Michael, “Body-Powered Components,” in Atlas of Amputations and Limb Deficiencies, 3rd ed., D. G. Smith, J. W. Michael, and J. H. Bowker, Eds. Rosemont, IL: American Academy of Orthopaedic Surgeons, 2004, pp. 131–143.
[10] D. D. Frey, L. E. Carlson, and V. Ramaswamy, “Voluntary-Opening Prehensors with Adjustable Grip force,” J. Prosthetics Orthot., vol. 7, no. 4, pp. 124–131, 1995.
[11] M. A. Leblanc and L. E. Carlson, “Adjustable prehension device (APD) for prosthetic hooks,” in International Conference on Prosthetics and Orthotics, 1992, p. 67, Chicago USA.
[12] 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.”
[13] D. Meeks and M. LeBlanc, “Preliminary assessment of three new designs of prosthetic prehensors for upper limb amputees,” Prosthet. Orthot. Int., vol. 12, pp. 41–45, 1988.
[14] S. Procter and M. LeBlanc, “Clinical Evaluation of a New Design Prosthetic Prehensor,” J. Prosthetics Orthot., vol. 3, no. 2, pp. 79–83, 1991.
[15] J. Kuniholm, “Body Powered Hook,” 2008. [Online]. Available: http://openprosthetics.org/.
[16] J. W. Sensinger, “Voluntary Opening – Closing Terminal Device Design,” in International Conference on Prosthetics and Orthotics, 2010, Leipzig Germany.
[17] M. A. Leblanc, D. Parker, and C. Nelson, “New designs for prosthetic prehensors,” in Proceedings of 9th Internat’l Symposium on External Control of Human Extremities, 1987, pp. 475–481.
[18] T. Sullivan and K. Siong Teh, “Design and fabrication of a hybrid body-powered prosthetic hand with voluntary opening and voluntary closing capabilities,” ASME International Mechanical Engineering Congress and Exposition. Denver, CO, pp. 1–8, 2011.
[19] B. D. Veatch, “A combination VO/VC terminal device with variable mechanical advantage,” Am. Acad. Orthot. Prosthetics, 2004.
[20] C. Light, P. H. Chappell, and P. J. Kyberd, “Establishing a Standardized Clinical Assessment Tool of Pathologic and Prosthetic Hand Function: Normative Data, Reliability, and Validity,” Arch. Phys. Med. Rehabil., vol. 83, pp. 776–783, 2002.
[21] K. Berning, S. Cohick, R. Johnson, and J. W. Sensinger, “Comparison of body-powered voluntary open and voluntary close prehensors for activities of daily living,” J. Rehabil. Res. Dev., vol. submitted, 2013.
[21] Sensinger J, Lipsey J, Thomas A, and Turner K (2015), "Design and evaluation of voluntary opening and closing prosthetic terminal device", Journal of Rehabilitation Researhc and Development.
[22] Sensinger J, Swartz A, and Lipsey J (2022). Lockable finger system and related methods. United States patent 11246721