Design and Preliminary Evaluation of a Two DOFs Cable-Driven Ankle–Foot Prosthesis with Active Dorsiflexion–Plantarflexion and Inversion–Eversion

Abstract

This paper describes the design of an ankle–foot robotic prosthesis controllable in the sagittal and frontal planes. The prosthesis was designed to meet the mechanical characteristics of the human ankle including power, range of motion, and weight. To transfer the power from the motors and gearboxes to the ankle–foot mechanism, a Bowden cable system was used. The Bowden cable allows for optimal placement of the motors and gearboxes in order to improve gait biomechanics such as the metabolic energy cost and gait asymmetry during locomotion. Additionally, it allows flexibility in the customization of the device to amputees with different residual limb sizes. To control the prosthesis, impedance controllers in both sagittal and frontal planes were developed. The impedance controllers used torque feedback from strain gages installed on the foot. Preliminary evaluation was performed to verify the capability of the prosthesis to track the kinematics of the human ankle in two degrees of freedom (DOFs), the mechanical efficiency of the Bowden cable transmission, and the ability of the prosthesis to modulate the impedance of the ankle. Moreover, the system was characterized by describing the relationship between the stiffness of the impedance controllers to the actual stiffness of the ankle. Efficiency estimation showed 85.4% efficiency in the Bowden cable transmission. The prosthesis was capable of properly mimicking human ankle kinematics and changing its mechanical impedance in two DOFs in real time with a range of stiffness sufficient for normal human walking. In dorsiflexion–plantarflexion (DP), the stiffness ranged from 0 to 236 Nm/rad and in inversion–eversion (IE), the stiffness ranged from 1 to 33 Nm/rad.

An Ankle-Foot Prosthesis for Rock Climbing Augmentation

“…The Empower ankle weighs 1928 grams [11]. Another powered prosthesis matches ankle kinematics about 2-DOF [13]. This prototype device uses a cable driven system to control joint position and torque about the anle and subtalar axis.…”

“…This prototype device uses a cable driven system to control joint position and torque about the anle and subtalar axis. However, this device weighs 3000 grams [13]. Powered walking prostheses are able to adjust joint position and torque, however current devices are heavy and do not provide the user with volitional control of the device.…”

Estimation of the Two Degrees-of-Freedom Time-Varying Impedance of the Human Ankle

“…BiOM [9] is an ankle-foot prosthesis capable of generating net positive work during plantarflexion. Ficanha et al recently developed an ankle-foot prosthesis with two powered degrees-of-freedom (DOF) in DP and inversion-eversion (IE) capable of injecting energy throughout the gait in those two DOF [10][11][12][13]. Active IE DOF has also been considered in an anklefoot prosthesis emulator by Collins et al [14].…”

Estimation of the 2-DOF Time-Varying Impedance of the Human Ankle

“…The platform allows the ankle impedance to be estimated at 250 Hz in both DP and IE, including combined rotations in both degrees of freedom (DOF) simultaneously. The results can be used in a 2-DOF powered ankle-foot prosthesis developed by the authors, which is capable of mimicking the ankle kinetics and kinematics in the frontal and sagittal planes [4]. The vibrating platform can also be used to tune the prosthesis to assure it properly mimics the human ankle dynamics.…”