Design and characterization of a biologically inspired quasi-passive prosthetic ankle-foot

Abstract

By design, commonly worn energy storage and release (ESR) prosthetic feet cannot provide biologically realistic ankle joint torque and angle profiles during walking. Additionally, their anthropomorphic, cantilever architecture causes their mechanical stiffness to decrease throughout the stance phase of walking, opposing the known trend of the biological ankle. In this study, the design of a quasi-passive pneumatic ankle-foot prosthesis is detailed that is able to replicate the biological ankle's torque and angle profiles during walking. The prosthetic ankle is comprised of a pneumatic piston, bending spring and solenoid valve. The mechanical properties of the pneumatic ankle prosthesis are characterized using a materials testing machine and the properties are compared to those from a common, passive ESR prosthetic foot. The characterization spanned a range of ankle equilibrium pressures and testing locations beneath the foot, analogous to the location of center of pressure within the stance phase of walking. The pneumatic ankle prosthesis was shown to provide biologically appropriate trends and magnitudes of torque, angle and stiffness behavior, when compared to the passive ESR prosthetic foot. Future work will focus on the development of a control system for the quasi-passive device and clinical testing of the pneumatic ankle to demonstrate efficacy.

Development and testing of a passive ankle exoskeleton

“…Another minimally powered foot prosthesis has been designed by Mooney et al [27]. The device uses a pneumatic piston as well as a bending spring in an attempt to closely mimic the stiffness of the biological ankle.…”

Volitional control of an active prosthetic ankle: a survey

“…In the same vein as Brackx et al 5 Mooney and his team found that the existing prosthetic ankles at their time were incapable of providing the amputee with "biologically realistic" ankle torque and angles. 7 They developed a quasi-passive ankle with pneumatic components. They compared their ankle with a passive ESR prosthetic foot.…”

“…All the test data was compared to the prosthesis that the test subjects used daily. Nickel et al 7 outlined user experience while wearing the prosthesis. The experimental data is shown in Figure 3 that compares kinematic and kinetic data from their prototype and the subject's prosthesis.…”

“…Unlike the articles before where the ankles were passive, Mooney et al developed a quasi-passive prosthetic ankle using a pneumatic piston-cylinder assembly. 7 This assembly seemed bulky and not useful for daily use. The fluctuation in internal pressure of the cylinder would cause a difference in the ankle's output.…”

“…Their use of hydraulic components in the system is just like. 7 The hydraulic system makes the ankle difficult to maintain. They explained their use of the hydraulic system well in their article.…”